Smoke test: a button click round-trips to D1 and rewrites its message

The phase-0 exit criterion, exercised in the real guild after cutover.

- [ ] Post a message with one button from the Worker.
- [ ] Click it: the interaction is verified, a row is written to D1, and the response is `UPDATE_MESSAGE` (type 7) rewriting *that* message.
- [ ] Click it again after 15 minutes to confirm the interaction-token lifetime is moot under send-only.
- [ ] Confirm an unknown `custom_id` degrades to the retired-post response, never to "interaction failed".
- [ ] Confirm a click routes through the per-session `SessionLock` Durable Object.

Start at the Worker entry point that posts the button and follow the click through interaction verification, the D1 write, the UPDATE_MESSAGE response, the unknown custom_id fallback, and the per-session SessionLock Durable Object. Run the phase-0 smoke test in the real guild, including the second click after 15 minutes; done means every checklist item passes.

Written by the indexing model from the issue text.