docs: Clarify documentation gaps across the project

[jmuzina]

Done

I'm leaving the project shortly, so I'm taking the opportunity to clarify some details and best practices that are mostly in my head or have become unspoken practice amongst Vanilla maintainers.

Check if PR is ready for release

If this PR contains Vanilla SCSS or macro code changes, it should contain the following changes to make sure it's ready for the release:

• PR should have one of the following labels to automatically categorise it in release notes:
  • Feature 🎁, Breaking Change 💣, Bug 🐛, Documentation 📝, Maintenance 🔨.
• Vanilla version in package.json should be updated relative to the most recent release, following semver convention
  • if existing APIs (CSS classes & macro APIs) are not changed it can be a bugfix release (x.x.X)
  • if existing APIs (CSS classes & macro APIs) are changed/added/removed it should be a minor version (x.X.0)
  • see the wiki for more details
• Any changes to component class names (new patterns, variants, removed or added features) or macros should be listed on the what's new page.

[webteam-app]

Demo

Jenkins

demos.haus

[Copilot]

Pull request overview

This PR enhances project documentation by clarifying best practices, workflows, and conventions for Vanilla Framework maintainers. The documentation consolidates previously undocumented practices into accessible GitHub guides, supporting better onboarding and consistency across the team.

Key Changes

• Introduced new documentation files for language policy and CI overview
• Enhanced Percy workflow and hacking guides with additional context about examples, testing, and naming conventions
• Documented class name prefixes, patterns vs components terminology, and standalone/combined example conventions

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 3 comments.

File	Description
guides/percy-workflow.md	Added cross-reference to hacking guide and tip about appending to combined.html files
guides/language.md	New file documenting en-US writing policy and mdspell usage
guides/hacking.md	Expanded with sections on examples relationship, combined examples, CI overview, patterns vs components, class prefixes, and language policy; fixed typo "name" → "named"
guides/ci.md	New comprehensive guide covering local checks, Percy, Jest, Parker, Cypress, and spelling

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