Fix AskUserQuestion UI, stop button, and orphaned conversation recovery

[charun-za]

Summary

• Fix AskUserQuestion tool showing as raw JSON permission dialog instead of interactive UI
• Fix stop button not killing Claude process on Windows (ghost processes, "Stream closed" errors)
• Add orphaned conversation recovery on startup

Changes

• Intercept AskUserQuestion inside can_use_tool flow and render interactive question card with radio/checkbox/free-text options
• Format answers as flat map for correct serialization
• Cancel pending question requests when process ends
• Run taskkill /t before abort() to kill full process tree (prevents orphaned children on Windows)
• Close stdin gracefully before force-killing process
• Add process generation counter to ignore output from killed processes
• Guard against spawning duplicate processes
• Add stream error handlers on stdin/stdout/stderr to prevent crashes
• Scan conversations directory on startup and re-index files missing from workspaceState
• Add CSS styles for question UI (options, submit button, answered/cancelled states)