matrix-intake: bot joins the email-review room on startup

room_send to a room the bot is only invited to (not joined) fails M_FORBIDDEN;
join explicitly on startup (idempotent if already a member). Bot-only change —
ships via the Spark git pull, no s9pk bump.

backend/matrix_intake/bot.py

@@ -275,6 +275,12 @@ async def main():
     print(f"matrix-intake: listening as {who.user_id} in room {intake_room}", flush=True)
     tasks = [asyncio.create_task(client.sync_forever(timeout=30000))]
     if review_room:
+        # "Invited" isn't "joined" — the bot must join before it can post cards (room_send to a
+        # room we're only invited to fails M_FORBIDDEN). Idempotent if already a member.
+        try:
+            await client.join(review_room)
+        except Exception as exc:
+            print(f"matrix-intake: could not join review room {review_room}: {exc}", flush=True)
         tasks.append(asyncio.create_task(poll_email_proposals()))
         print(f"matrix-intake: reviewing email proposals in room {review_room} (every {EMAIL_POLL_SEC}s)", flush=True)
     try: