Fix webview lockup on startup by adding loading state and retry logic

[roomote]

This PR fixes issue #6234 where Roo Code would completely lock up on startup, showing only a scrolling bar at the top and a blank screen.

Problem

The webview was returning null when didHydrateState was false, resulting in a blank screen if the extension was slow to respond with the initial state. This left users with an unresponsive plugin.

Solution

1. Created LoadingScreen component - Shows a proper loading state with VS Code progress ring instead of blank screen
2. Added timeout handling - Displays a message when loading takes longer than expected (10 seconds)
3. Implemented retry logic - Both App and ExtensionStateContext now retry sending the initialization message if no response is received within 2 seconds
4. Changed rendering behavior - App now renders LoadingScreen instead of null when waiting for state hydration

Testing

• All existing tests pass
• The loading screen provides immediate visual feedback
• Retry mechanism ensures the extension eventually connects even if the initial message is missed
• Timeout message helps users understand when something might be wrong

Fixes #6234

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Important

Fixes webview lockup on startup by adding a loading screen, timeout handling, and retry logic in App.tsx, LoadingScreen.tsx, and ExtensionStateContext.tsx.

• Behavior:
  • App.tsx: Renders LoadingScreen instead of null when didHydrateState is false.
  • LoadingScreen.tsx: New component with a progress ring and optional timeout message.
  • ExtensionStateContext.tsx: Implements retry logic for webviewDidLaunch message if no response in 2 seconds.
• Timeout Handling:
  • App.tsx: Shows timeout message after 5 seconds if state not hydrated.
  • App.tsx: Retries sending webviewDidLaunch after 3 seconds if state not hydrated.
• Testing:
  • All existing tests pass.
  • Loading screen provides immediate feedback.
  • Retry mechanism ensures eventual connection.
  • Timeout message informs users of potential issues.

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[ellipsis-dev]

User-facing text ('Loading Roo Code...' and 'Taking longer than expected...') is hardcoded. Consider using translation functions to support internationalization as per our guidelines.

^{This comment was generated because it violated a code review rule: irule_C0ez7Rji6ANcGkkX.}

[daniel-lxs]

Not sure if it works but closing for now while we scope the issue