feat(plugin): file watcher for completion detection and auto-reload

[JeremyDev87]

Purpose

Watch file system for changes instead of polling via capture-pane. Detect worker completion (RESULT.json), rule changes (.ai-rules/), and config changes instantly.

Changes

• packages/codingbuddy-plugin/ — File watcher module (chokidar or fs.watch)

Key Watchers

• .taskmaestro/wt-N/RESULT.json → worker completion instant detection
• packages/rules/.ai-rules/ → auto-reload rules on change
• codingbuddy.config.json → auto-reload config on change

Supersedes

• taskMaestro: add worker completion signaling mechanism #767 (completion signaling) — File watcher replaces polling

Acceptance Criteria

• Watch RESULT.json for worker completion
• Watch .ai-rules/ for rule changes → auto-reload
• Watch config for settings changes → auto-reload
• Debounced to avoid excessive triggers