Add reversible administrator room archiving

Organize closed rooms with archive filters, live-authorized atomic receipts and exact saved retries. Preserve saved games, timestamps, credentials, discussion and AI deadlines. Unarchive leaves play closed; reopen requires unarchive, and removal/restoration preserves both flags.

Verified types, lint, 5379 offline tests, 52 HTTP tests and build. Twenty dedicated administrator HTTP groups and independent privacy/persistence review passed. Desktop/mobile browser QA confirmed a single archive after a lost response and refresh, readable recovery text, mobile unarchive and separate reopening, and saved-seat restoration. All 2,049 baseline rooms, 4,348 seats and related records preserved. Authenticated production admin acceptance awaits authorized QA access; full admin and rules gates remain open.

README.md

@@ -50,8 +50,10 @@ seats and host assignment without private seat access.
 [Remove or restore](docs/ADMIN_ROOM_REMOVAL.md) recoverably removes selected rooms;
 use the Directory filter to find them for restoration.
 [Close or reopen](docs/ADMIN_ROOM_CLOSURE.md) stops further play while preserving
-readable tables and history, then resumes the same saved position. Archive,
-permanent deletion, participant support and backup tools are still being built.
+readable tables and history, then resumes the same saved position.
+[Archive or unarchive](docs/ADMIN_ROOM_ARCHIVE.md) organizes closed rooms while
+retaining their tables and history; unarchiving leaves play closed.
+Permanent deletion, participant support and backup tools are still being built.
 
 ## Saved seats and reconnecting