feat(ui): support draggable tab reordering with stable dom ordering

[rust17]

Overview
This PR implements drag-and-drop reordering for both top-level database session tabs and internal workspace tabs (Data, Query, and Structure views). It also introduces a critical technical convention to ensure the stability of complex components like the Monaco Editor during UI reordering.

Key Changes

• Draggable Tabs: Users can now drag and drop tabs to reorder them, similar to the behavior in VS Code.
• useDraggableSort Hook: Extracted reusable drag-and-drop logic into a custom hook to handle state management (draggedIdx, dragOverIdx), event handlers, and visual drop indicators.
• Stable DOM Ordering: Resolved a critical crash in Monaco Editor (InstantiationService has been disposed) by decoupling the UI display order from the physical DOM order.
• Documentation: Added the "UI Rendering Stability" convention to AGENTS.md to prevent similar regressions in the future.