fix: store version in gitignored .local_version to prevent notification spam (bd-tok)

Root cause: metadata.json is tracked in git and contains last_bd_version.
When git operations (pull, checkout, merge) reset metadata.json to the
committed version, the upgrade notification would fire repeatedly.

Fix: Store the last used bd version in .beads/.local_version which is
gitignored, so git operations don't affect version tracking.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

.beads/.gitignore

@@ -11,6 +11,10 @@ daemon.log
 daemon.pid
 bd.sock
 
+# Local version tracking (prevents upgrade notification spam after git operations)
+# bd-tok: Store version locally instead of in tracked metadata.json
+.local_version
+
 # Legacy database files
 db.sqlite
 bd.db