feat: implement workspace-specific index settings storage

[roomote]

Implements workspace-specific storage for index settings to fix issue #6406.

Key changes:

• Extended ContextProxy with workspace storage methods
• Updated CodeIndexConfigManager to use workspace storage
• Added automatic migration from global to workspace settings
• Updated webview message handler for per-workspace saving
• Added comprehensive tests for new functionality

This allows different workspaces to have different vector database configurations, which is especially useful when switching between local development and dev containers.

Fixes #6406

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Important

Implements workspace-specific storage for index settings, enabling distinct configurations per workspace and automatic migration from global settings.

• Behavior:
  • Implements workspace-specific storage for index settings in ContextProxy and CodeIndexConfigManager.
  • Adds automatic migration from global to workspace settings if workspace settings are absent.
  • Updates webviewMessageHandler to handle per-workspace saving of settings.
• Tests:
  • Adds tests in config-manager.spec.ts to verify workspace-specific storage, migration, and preference over global settings.
• Misc:
  • Fixes issue Index settings do save based on workspace setting #6406 by allowing different workspaces to have distinct vector database configurations.

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[roomote]

Code Review Summary

This PR successfully implements workspace-specific storage for index settings, addressing issue #6406. The implementation includes proper migration from global to workspace settings and comprehensive test coverage.

Critical Issues (Must Fix):

1. Missing error handling in ContextProxy.updateWorkspaceState() - The method at lines 143-145 in src/core/config/ContextProxy.ts doesn't handle potential failures. Could this fail silently if workspace state update fails?

Important Suggestions (Should Consider):

2. Inconsistent migration behavior - In src/services/code-index/config-manager.ts lines 47-53, the migration from global to workspace happens every time workspace config is missing. Should this be a one-time operation instead?

3. Potential race condition - In src/core/webview/webviewMessageHandler.ts lines 1993-2012, the workspace state read and write operations aren't atomic, which could lead to data loss if multiple saves happen concurrently.

4. Test coverage gap - The new workspace storage methods in ContextProxy.ts (lines 136-145) lack direct unit tests, only integration tests exist.

Minor Improvements (Nice to Have):

5. Code duplication - The default configuration object in src/services/code-index/config-manager.ts lines 56-65 is duplicated and could be extracted to a constant.

6. Missing JSDoc documentation - The new workspace methods in ContextProxy.ts would benefit from JSDoc comments for better API discoverability.

Positive Notes:

• Excellent test coverage for the workspace-specific functionality
• Clean migration strategy from global to workspace settings
• Proper handling of fallback scenarios
• Implementation correctly addresses the user's need for different configurations per workspace

Overall, this is a solid implementation that solves the core issue effectively. The critical error handling issue should be addressed, but the functionality works as intended.

[daniel-lxs]

Closing, see #6406 (comment)