feat(vscode): add read/write plan tools and UI integration

[godtail]

This PR introduces new capabilities for the agent to interact with plan files directly through the VSCode extension. It adds readPlan and writeToPlan tools, allowing the agent to read context from and append updates to plan documents. The changes also include full UI integration for these tools in the chat interface and comprehensive unit tests.

Changes

🛠️ Tooling (packages/tools)

• Added readPlan and writeToPlan tool definitions.
• Updated types.ts and index.ts to export the new tools.

🔌 VSCode Extension (packages/vscode)

• Implemented handlers for readPlan and writeToPlan.
• Registered new tools in vscode-host-impl.ts.
• Added unit tests:
  • packages/vscode/src/tools/__test__/read-plan.test.ts
  • packages/vscode/src/tools/__test__/write-to-plan.test.ts

💻 WebUI (packages/vscode-webui)

• Updated CreateTaskInput and tool call lifecycle management to support the new plan tools.
• Added Plan tools to the settings configuration (tools-section.tsx).
• Updated localization files (en, jp, ko, zh) with new strings.

🌉 Common (packages/common)

• Updated webview bridge definitions in webview.ts.

Testing

• Verified with new unit tests in packages/vscode.
• Manual testing required to verify UI integration and tool execution flow in the VSCode extension.