Drop the lock file: too much machinery for a personal CLI

Concurrent runs of the CLI can again lose an update; saves stay atomic.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

.gitignore

@@ -1,7 +1,6 @@
 node_modules/
 todos.json
 *.tmp
-*.lock
 .DS_Store
 
 # Personal Claude Code overrides (not shared)