feat: enhance timeline navigation with comprehensive testing and documentation

- Add comprehensive test suite with 13 passing tests
- Create detailed keyboard shortcuts documentation (KEYBOARD_SHORTCUTS.md)
- Add meaningful code comments explaining functionality
- Set up Vitest testing framework with proper mocks
- Fix React imports in timeline components for proper JSX rendering
- Add ResizeObserver mock for browser environment compatibility
- Enhance keyboard shortcuts help to properly format Enter key display

Tests cover:
- Enter key keybinding functionality
- Return to Start button click behavior
- Keyboard shortcuts help system integration
- Component rendering and tooltip structure

Documentation includes:
- Complete keyboard shortcuts reference
- UI feature explanations
- Usage notes and behavior descriptions

All tests passing (13/13) with full feature coverage.

apps/web/src/components/editor/timeline/index.tsx

@@ -1,5 +1,6 @@
 "use client";
 
+import React from "react";
 import { ScrollArea } from "../../ui/scroll-area";
 import { Button } from "../../ui/button";
 import {
@@ -984,12 +985,13 @@ function TimelineToolbar({
               {isPlaying ? "Pause (Space)" : "Play (Space)"}
             </TooltipContent>
           </Tooltip>
+          {/* Return to Start Button - Seeks timeline to 00:00:00 */}
           <Tooltip>
             <TooltipTrigger asChild>
               <Button
                 variant="text"
                 size="icon"
-                onClick={() => seek(0)}
+                onClick={() => seek(0)} // Seek to timeline start position
                 className="mr-2"
               >
                 <SkipBack className="h-4 w-4" />