feat(ai): name agents after their model, not hardcoded "oracle"

Agents now join under their model tag (e.g. "qwen2.5:3b" — model name +
parameter size) or profile label, derived at /ai start and tracked on
App.agent_name, so the roster shows what's actually answering. Updates the
broker re-grant + /ai stop revoke paths, the Python --name default
(falls back to provider.model), and the demo/bootstrap/README/docs refs.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

bootstrap-ai.sh

@@ -129,6 +129,6 @@ fi
 echo
 echo "AI ready. start a local agent against a running room with:"
 echo "    .venv/bin/python -m cmd_chat.agent <host> <port> \\"
-echo "        --name oracle --password <room-pw> --provider ollama --model $MODEL --no-tls"
+echo "        --password <room-pw> --provider ollama --model $MODEL --no-tls"
 echo
 echo "tip: pick a different model with  HH_AI_MODEL=llama3 ./bootstrap-ai.sh"