feat(register): auto hot-reload service after channel register/deregister

Making a channel registration live no longer depends on an operator/agent
remembering to restart. setup/register.ts and scripts/deregister-room.ts now
call signalEjclawReload() after the DB write, which sends SIGHUP to the running
service's main PID (→ runtimeState.reloadRoomBindings). Best-effort and
injectable-for-tests; no-ops when the service isn't running.

Also document the canonical rule in the committed, agent-loaded platform prompt
(prompts/claude-platform.md): prefer these paths, never fake a restart, verify
via the "Room bindings reloaded" log; a plain in-turn systemctl restart is
forbidden (it kills the agent).

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

scripts/deregister-room.ts

@@ -34,6 +34,7 @@ import path from 'path';
 import { Database } from 'bun:sqlite';
 
 import { DATA_DIR, GROUPS_DIR, STORE_DIR } from '../src/config.js';
+import { signalEjclawReload } from '../src/runtime-reload-signal.js';
 
 const args = process.argv.slice(2);
 const dryRun = args.includes('--dry-run');
@@ -355,5 +356,15 @@ try {
   /* ignore */
 }
 
-console.log('\nDone. Restart ejclaw to drop the room(s) from live bindings:');
-console.log('  systemctl --user restart ejclaw.service');
+// Make the deregistration live immediately by hot-reloading the running
+// service's room bindings (no full restart needed).
+const reloaded = signalEjclawReload();
+if (reloaded) {
+  console.log(
+    '\nDone. Signaled ejclaw to hot-reload room bindings (SIGHUP) — the room(s) are now dropped from live bindings.',
+  );
+} else {
+  console.log(
+    '\nDone. ejclaw was not running (or MainPID unavailable); the change applies on next start.',
+  );
+}