Database Availability Improvements

New database availability checking

• Added Wv() function to check if the database is available before attempting database operations
• All database-dependent functions now check availability first and return empty results if unavailable
• Added helpful error message (q90()) that explains when the database is unavailable:

  Database is not available. Continue/resume features are disabled.
  This is likely due to issues with the better-sqlite3 dependency.
  To fix: Try globally reinstalling better-sqlite3 with your package manager.
  For more detail, see: https://github.com/WiseLibs/better-sqlite3/blob/master/docs/troubleshooting.md

This means if you have issues with the better-sqlite3 dependency, Claude Code will now gracefully degrade instead of crashing. Features like conversation history and continue/resume will be disabled, but the core functionality will still work.