Refactor plan interface: synchronous in-thread planning with auto-issue creation

[oldsj]

Problem

Current plan interface assumes questions as a response and the async approach doesn't really work. Planning shouldn't be an async background task.

Proposed Flow

1. In-thread planning: When planning is needed, main thread takes over like Claude Code's plan mode

   • Main thread needs repo access (ideally via fast, up-to-date cache)
   • Back-and-forth happens synchronously in the conversation
   • Similar to how Claude Code detects you need plan mode and switches

2. Context compression: After planning completes, compress/summarize the planning context

   • Avoids polluting the main thread with verbose planning details
   • Main thread gets a clean summary of what was decided

3. Auto-issue creation: Once user approves the plan

   • Automatically create a GitHub issue on the appropriate repo
   • Apply correct labels
   • Return to main conversation

Why Synchronous

• Planning requires back-and-forth dialogue
• Async creates awkward UX (waiting, context switching)
• User needs to be engaged during planning, not after

Key Considerations

• How to give main thread fast repo access (caching strategy?)
• Context compression approach (what to preserve vs summarize)
• Repo detection for auto-issue creation
• Label inference/selection
• Transition UX (entering/exiting plan mode)

Acceptance Criteria

• Planning happens synchronously in main thread
• Repo context available without slow fetches
• Planning context compressed after completion
• Approved plans auto-create GitHub issues with labels
• Smooth return to main conversation