Add Tasks panel infrastructure with type-safe IPC protocol

[EhabY]

Summary

Build the foundational infrastructure for the Tasks panel, focusing on the backend panel class and a type-safe communication layer between the webview and extension.

Goals

• Create TasksPanel backend with task operations, log caching, and push notifications
• Establish a type-safe IPC protocol for webview-extension communication that catches contract mismatches at compile time
• Set up supporting test infrastructure and tooling for webview development

Resources

• Figma designs
• Notion spec