fix: use actual nio device_id in call.member events, not hardcoded AIBOT

Element X sends E2EE keys via encrypted to-device messages targeting
the device_id from the call.member state event. Bot was advertising
device_id='AIBOT' but its actual Matrix session is on device
'PEYRKFEXFP'. Keys were sent to a non-existent device.

Now uses the real device_id from nio credentials so Element X's
encryptAndSendToDevice reaches the correct device.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

bot.py

@@ -49,7 +49,7 @@ from cron import CronScheduler
 from device_trust import CrossSignedOnlyPolicy
 from cross_signing import CrossSigningManager
 
-BOT_DEVICE_ID = "AIBOT"
+BOT_DEVICE_ID = os.environ.get("BOT_DEVICE_ID", "AIBOT")  # Overridden at login with actual nio device_id
 CALL_MEMBER_TYPE = "org.matrix.msc3401.call.member"
 ENCRYPTION_KEYS_TYPE = "io.element.call.encryption_keys"
 
@@ -1314,6 +1314,9 @@ class Bot:
             )
             self.client.load_store()
             logger.info("Restored session as %s (device %s)", creds["user_id"], creds["device_id"])
+            # Use actual device ID for call.member events so to-device keys arrive correctly
+            global BOT_DEVICE_ID
+            BOT_DEVICE_ID = creds["device_id"]
         else:
             resp = await self.client.login(BOT_PASS, device_name="ai-voice-bot")
             if not isinstance(resp, LoginResponse):
@@ -1327,6 +1330,8 @@ class Bot:
                     "access_token": resp.access_token,
                 }, f)
             logger.info("Logged in as %s (device %s) — credentials saved", resp.user_id, resp.device_id)
+            # Use actual device ID for call.member events
+            BOT_DEVICE_ID = resp.device_id
 
         if self.client.should_upload_keys:
             await self.client.keys_upload()