Prototype administrative discussion mute controls

Let owners/operators mute or unmute new public/private sends from a human seat while retaining history, incoming messages, gameplay and credentials. Fence metadata and durable audit writes with live authority, membership and versions. Preserve exact admin/message retries and inherit restrictions through seat recovery.

Validation: types/lint, 5431 offline tests, build, 52 HTTP integration tests, 24 administrator HTTP groups, independent SQL/privacy/UI review and desktop/mobile refresh acceptance. All 2230 prior games and 4746 seats preserved. Additive migration 0016. Verified runtime fingerprint 588967fbb9c2e3b6abe2990c4fce96ee69e2256fb7e3ee416314b87593cebba9; documentation-only grammar/button-label review gives b5e57bdd26812debede91c588e38f247f1fa895ad23e7ae30bc8550eedcd90ec. New-revision deployed acceptance remains open; full admin/rules scope is unfinished.

README.md

@@ -54,8 +54,10 @@ 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.
 [Participant AI](docs/ADMIN_PARTICIPANT_AI.md) supports an absent human in a paused
-game while preserving their seat and takeback control. Permanent deletion,
-further participant support and backup tools are still being built.
+game while preserving their seat and takeback control.
+[Discussion controls](docs/ADMIN_DISCUSSION.md) mute or unmute new messages from
+a human seat while preserving history and gameplay. Permanent deletion, further
+participant support and backup tools are still being built.
 
 ## Saved seats and reconnecting