Report build starts and successes, not just failures, to their own chat

Only failures were reported, so a push could reach the mirror with no way to
know short of querying the database by hand. Release runs now report:

- start: channel, arch, host, and the commit being built
- published: the packages and versions that went out, duration, channel URL
- no-changes: the run found nothing to build
- promoted: what advance moved between channels, including the rc bootstrap
  and fast-ring replication
- failed: unchanged, plus the commit context the other reports carry

Release traffic goes to OMARCHY_RELEASE_CHATBOT_URL, falling back to
BASECAMP_CHATBOT_URL, so build reports stop drowning the repository chat the
sync workflows post to. bin/setup reports which destination is configured.

The published list is captured after the build step because promote moves the
files out of build-output, and is capped at 25 entries so a full rebuild does
not produce an unreadable wall of chat.

README.md

@@ -756,6 +756,31 @@ That cadence is only safe because of three guards:
 `bin/repo timers` reports all of this: schedules, last results, what is
 queued, what is failing and when it will retry, and whether the lock is held.
 
+### Build reports
+
+Every release run reports to Basecamp Campfire — not just failures, so a push
+can be followed all the way to the mirror without watching the host:
+
+| Event | Message |
+|---|---|
+| 🔨 Started | channel, arch, host, and the commit being built |
+| ✅ Published | the packages and versions that went out, duration, and the channel URL |
+| 📦 Promoted | what `advance` moved between channels (including the rc bootstrap and fast-ring replication) |
+| 📦 No changes | the run found nothing to build |
+| 🔴 Failed | which step failed, the commit, and the last 25 log lines |
+
+Release traffic gets its own chat so it does not drown the repository chat
+that the AUR/upstream sync workflows post to. Export the destination in
+`/root/.omarchy/build-credentials`:
+
+```bash
+export OMARCHY_RELEASE_CHATBOT_URL="https://3.basecamp.com/<account>/integrations/<key>/buckets/<project>/chats/<chat>/lines"
+```
+
+Without it, release reports fall back to `BASECAMP_CHATBOT_URL`; with neither
+set they are silently skipped. `bin/setup` reports which of the three cases
+applies.
+
 Check on all of it with `bin/repo timers` — schedule, each unit's last run and
 whether it succeeded, what is queued, whether a release is running right now,
 and any failed units. Like the other host commands it forwards over ssh, so