docs: updated documentation of reactive-controllers (#5802)

* docs: updated documentation of reactive-controllers

* docs: updated main readme to align with doc standard

* docs: updated color controller readme to align with doc standard

* docs: updated dependency controller readme to align with doc standard

* docs: updated element resolution controller readme to align with doc standard

* docs: updated match media controller readme to align with doc standard

* docs: updated pending state controller readme to align with doc standard

* docs: updated pending roving tab index controller readme to align with doc standard

* docs: updated the element resolution example with form field logic

* docs: updated element resolution modal overlay example to show the usage pattern

* docs: added new language resolution controller readme

* docs: removed commented code in main readme

* docs: update docs for the disabled items in robing tab index controller

* docs: removed screen reader section in roving tab index

* chore: fix up review comments on verbs and script tags

* chore: added system context controller readme

* chore: main readme formatting fix

---------

Co-authored-by: Rajdeep Chandra <rajdeepchandra@Rajdeeps-MacBook-Pro-7.local>
Co-authored-by: Rajdeep Chandra <rajdeepchandra@rajdeeps-mbp-7.macromedia.com>
Co-authored-by: Rajdeep Chandra <rajdeepchandra@rajdeeps-mbp-8.macromedia.com>
Co-authored-by: Rajdeep Chandra <rajdeepchandra@Rajdeeps-MacBook-Pro-8.local>
Co-authored-by: Rajdeep Chandra <rajdeepc@adobe.com>

Author: 6 people

1st-gen/tools/reactive-controllers/README.md

@@ -1,14 +1,270 @@
-## Description
+## Overview
 
-[Reactive controllers](https://lit.dev/docs/composition/controllers/) are a tool for code reuse and composition within [Lit](https://lit.dev), a core dependency of Spectrum Web Components. Reactive controllers can be reused across components to reduce both code complexity and size, and to deliver a consistent user experience. These reactive controllers are used by the Spectrum Web Components library and are published to NPM for you to leverage in your projects as well.
+[Reactive controllers](https://lit.dev/docs/composition/controllers/) are a powerful tool for code reuse and composition within [Lit](https://lit.dev), a core dependency of Spectrum Web Components. They enable you to extract common behaviors into reusable packages that can be shared across multiple components, reducing code complexity and size while delivering a consistent user experience.
 
-### Reactive controllers
+### Usage
 
--   [ColorController](../color-controller)
--   [ElementResolutionController](../element-resolution)
--   FocusGroupController
--   LanguageResolutionController
--   [MatchMediaController](../match-media)
--   [RovingTabindexController](../roving-tab-index)
--   [PendingStateController](../pending-state)
--   SystemContextResolutionController
+```bash
+yarn add @spectrum-web-components/reactive-controllers
+```
+
+Reactive controllers are instantiated in your component and automatically hook into the component's lifecycle:
+
+```typescript
+import { LitElement, html } from 'lit';
+import { MatchMediaController } from '@spectrum-web-components/reactive-controllers/src/MatchMedia.js';
+
+class MyComponent extends LitElement {
+    // Create controller instance
+    darkMode = new MatchMediaController(this, '(prefers-color-scheme: dark)');
+
+    render() {
+        // Use controller state in render
+        return html`
+            <div class=${this.darkMode.matches ? 'dark' : 'light'}>Content</div>
+        `;
+    }
+}
+```
+
+### Controller lifecycle
+
+Reactive controllers implement the `ReactiveController` interface with the following optional lifecycle methods:
+
+- **`hostConnected()`**: Called when the host element is connected to the DOM
+- **`hostDisconnected()`**: Called when the host element is disconnected from the DOM
+- **`hostUpdate()`**: Called before the host's `update()` method
+- **`hostUpdated()`**: Called after the host's `update()` method
+
+Controllers can also call `host.requestUpdate()` to trigger an update cycle on the host element.
+
+### Creating your own controllers
+
+You can create custom reactive controllers by implementing the `ReactiveController` interface:
+
+```typescript
+import { ReactiveController, ReactiveElement } from 'lit';
+
+export class MyController implements ReactiveController {
+    private host: ReactiveElement;
+
+    constructor(host: ReactiveElement) {
+        this.host = host;
+        // Register this controller with the host
+        this.host.addController(this);
+    }
+
+    hostConnected() {
+        // Called when host is connected to DOM
+    }
+
+    hostDisconnected() {
+        // Called when host is disconnected from DOM
+    }
+}
+```
+
+### Available controllers
+
+#### ColorController
+
+Manages and validates color values in various color spaces (RGB, HSL, HSV, Hex). Provides conversion between formats and state management for color-related interactions.
+
+**Use cases:**
+
+- Color pickers and selectors
+- Color input validation
+- Color format conversion
+- Theme customization UIs
+
+**Key features:**
+
+- Multiple color format support (hex, RGB, HSL, HSV)
+- Color validation
+- Format preservation
+- Undo/redo support
+
+[Learn more →](../color-controller)
+
+---
+
+#### DependencyManagerController
+
+Manages the availability of custom element dependencies, enabling lazy loading patterns and progressive enhancement strategies.
+
+**Use cases:**
+
+- Code splitting and lazy loading
+- Progressive enhancement
+- Route-based component loading
+- Conditional feature loading
+
+**Key features:**
+
+- Tracks custom element registration
+- Reactive loading state
+- Multiple dependency management
+- Works with dynamic imports
+
+[Learn more →](../dependency-manager)
+
+---
+
+#### ElementResolutionController
+
+Maintains an active reference to another element in the DOM tree, automatically tracking changes and updating when the DOM mutates.
+
+**Use cases:**
+
+- Accessible label associations
+- Focus trap management
+- Form validation connections
+- Dynamic element relationships
+
+**Key features:**
+
+- Automatic DOM observation
+- ID selector optimization
+- Shadow DOM support
+- Reactive updates
+
+[Learn more →](../element-resolution)
+
+---
+
+#### FocusGroupController
+
+Base controller for managing keyboard focus within groups of elements. Extended by `RovingTabindexController` with tabindex management capabilities.
+
+**Use cases:**
+
+- Custom composite widgets
+- Keyboard navigation patterns
+- Focus management
+
+**Key features:**
+
+- Arrow key navigation
+- Configurable direction modes
+- Focus entry points
+- Element enter actions
+
+**Note:** This controller is typically not used directly. Use [RovingTabindexController](../roving-tab-index) instead for most use cases.
+
+---
+
+#### LanguageResolutionController
+
+Resolves and tracks the language/locale context of the host element, responding to changes in the `lang` attribute up the DOM tree.
+
+**Use cases:**
+
+- Internationalization (i18n)
+- Localized content
+- RTL/LTR text direction
+- Locale-specific formatting
+
+**Key features:**
+
+- Automatic language detection
+- Locale change tracking
+- Supports Shadow DOM
+- Bubbles up DOM tree
+
+[Learn more →](../language-resolution)
+
+---
+
+#### MatchMediaController
+
+Binds CSS media queries to reactive elements, automatically updating when queries match or unmatch.
+
+**Use cases:**
+
+- Responsive design
+- Dark mode detection
+- Mobile/desktop layouts
+- Print styles
+- Accessibility preferences (prefers-reduced-motion, etc.)
+
+**Key features:**
+
+- Multiple media query support
+- Reactive updates
+- Predefined queries (DARK_MODE, IS_MOBILE)
+- Event-driven
+
+[Learn more →](../match-media)
+
+---
+
+#### PendingStateController
+
+Manages pending/loading states for interactive elements, providing visual feedback and accessible state communication.
+
+**Use cases:**
+
+- Async button actions
+- Form submission states
+- Loading indicators
+- Progress feedback
+
+**Key features:**
+
+- Automatic ARIA label management
+- Progress circle rendering
+- Label caching and restoration
+- Disabled state awareness
+
+**Note:** Currently used primarily by Button component. May be deprecated in future versions.
+
+[Learn more →](../pending-state)
+
+---
+
+#### RovingTabindexController
+
+Implements the W3C ARIA roving tabindex pattern for keyboard navigation in composite widgets, managing `tabindex` attributes and arrow key navigation.
+
+**Use cases:**
+
+- Toolbars
+- Tab lists
+- Menus
+- Radio groups
+- Listboxes
+- Grids
+
+**Key features:**
+
+- Arrow key navigation (with Home/End support)
+- Automatic tabindex management
+- Flexible direction modes (horizontal, vertical, both, grid)
+- Skips disabled elements
+- WCAG compliant
+
+[Learn more →](../roving-tab-index)
+
+---
+
+#### SystemContextResolutionController
+
+Resolves and tracks system-level context like color scheme and scale preferences from Spectrum theme providers.
+
+**Use cases:**
+
+- Theme integration
+- Design system variant detection (Spectrum Classic, Express, Spectrum 2)
+- System-specific asset loading
+- Adaptive UI rendering
+
+**Key features:**
+
+- Automatic theme context resolution
+- Reactive system variant updates
+- Event-based communication with `<sp-theme>`
+- Automatic cleanup on disconnect
+
+**Note:** Private Beta API - subject to changes.
+
+[Learn more →](../system-context-resolution)