Add durable public and private table discussion

Humans can discuss plans publicly or message another human seat privately while
pending game decisions stay intact. The conversation panel provides plain text,
explicit recipient names and factions, saved history, private pagination and
exact retries through refresh. Human AI-control owners can still talk; bots do
not interpret messages or negotiate. Existing game actions execute agreements.

An additive indexed D1 message table stores discussion separately from game JSON,
versioning, readiness and bot continuation. Every read/insert checks active seat
credentials and membership; direct audiences and cursor lookups are filtered
before limiting. Public history has no private activity counts or sequential IDs.
Recovery/handover inherits seat history while fencing old credentials.

Independent review found two retry races: a rotation between a committed insert
and receipt read, and stale unmounted completion deleting a newer retry record.
Both are fixed with regressions. A prior uncertain retry stays pending on later
rejection. The nine focused offline cases and two HTTP cases cover production SQL,
concurrent/altered receipts, audience/cursor privacy, rotation/membership races,
actual saved-kit recovery and unchanged sealed setup state.

Types, lint, all 4963 offline tests, production build and 48 HTTP tests
pass on stable source. An initial check caught an invalid checklist status label;
that was corrected before the successful final2 verification.

Desktop browser checks send public/private messages, receive a peer reply, retain
private history after refresh and remove it on channel switch. Literal markup and
URLs remain text. Recipient and bystander API reads confirm the browser messages'
audiences. Screenshot capture was unavailable and the viewport override did not
take effect; mobile, full keyboard/visual and injected browser network-failure
acceptance remain open. No final rules, mode, AI or publication gate changes.

All 1373 pre-existing rooms, 2883 seats and auxiliary rows
are unchanged. SQLite integrity/foreign keys pass; migration 0007 adds messages
without replacing data. The healthy server was reused without restart.

Private evidence: 20260921-table-talk.
Verified source tree: 236dd55b6c15d55dbced735be67427e5fbd7fa348d583f119e67a03894ec21b0

README.md

@@ -51,6 +51,12 @@ An uncertain saved-kit recovery keeps its exact retry details in memory and prev
 
 Use **Pass your seat to another player** for a voluntary one-time transfer. The private offer lasts 24 hours; acceptance preserves progress and revokes the old owner’s sessions and recovery kits. The recipient uses **Accept a seat handover** on the home page, then creates their own recovery kit. Keep the tab open until acceptance is confirmed; exact private retry details survive refresh in that tab. See [seat handover](docs/SEAT_HANDOVER.md) for cancellation, retry behavior and current limits.
 
+Use **Table discussion** below the board for public conversation or private
+messages to another human seat. Messages survive refresh; exact retries avoid
+duplicates. Private history follows the seat through recovery or handover.
+Messages do not execute game actions, and AI opponents do not answer them yet.
+See [table discussion](docs/TABLE_DISCUSSION.md).
+
 The table header offers optional **Sound effects**, with mute, volume and a test
 sample. Short cues mark phase changes and automatic action notices. Sound starts
 off; preferences stay in your browser. See [table sounds](docs/TABLE_SOUNDS.md)