v1.5.3: FSEvents watch loop performance fixes

⚡ Performance

Daemon CPU usage reduced from ~40% sustained to ~2% idle.

Root causes fixed

• Home directory FSEvents — ~/.cursorrules sits directly in ~, causing watchdog to observe the entire home directory recursively. Every Claude transcript append, atuin history write, and cache update fired into the event queue. Fixed by skipping Path.home() as a watch root.
• Write-loop — sync writes to skill/settings destination paths, FSEvents picks those up before watch state is refreshed, re-triggers sync immediately. Fixed by draining the event queue after each sync.
• Expensive skill hashing — _skill_dir_hash was calling read_bytes() on every file in every skill dir every 3 seconds. Replaced with mtime+size stat — same change detection, no file reads.
• Transcript FSEvents — ~/.claude/projects/ and ~/.codex/sessions/ were watched by FSEvents; active sessions write every few seconds, each triggering a 360ms rglob. Moved history sync to a 60s periodic timer.