1. CRITICAL: Permission overwrites now properly merge instead of replace.
set_permissions with keyword args REPLACES the entire overwrite,
so Lock→Hide would undo the Lock. Now uses overwrites_for() to
fetch existing state and modify only the target field.
Affects: Lock, Unlock, Hide, Unhide, Ghost, Reveal (buttons & commands)
2. CRITICAL: Removed broken async generator in any() for game rename check.
await in generator expression creates async generator that any() can't
consume. Game rename loop now always starts and checks config per-guild.
3. Minor: Fixed double-write in _save_temp_channels.
4. Minor: Removed unused imports (datetime, Set).
