Add Rich token streaming: server SSE + CLI live display + CLI container

Server (agent.py):
- _stream_queues: per-session asyncio.Queue for token chunks
- _push_stream_chunk() / _end_stream() helpers
- Medium tier: astream() with <think> block filtering — real token streaming
- Light tier: full reply pushed as single chunk then [DONE]
- Complex tier: full reply pushed after agent completes then [DONE]
- GET /stream/{session_id} SSE endpoint (data: <chunk>\n\n, data: [DONE]\n\n)
- medium_model promoted to module-level global for astream() access

CLI (cli.py):
- stream_reply(): reads /stream/ SSE, renders tokens live with Rich Live (transient)
- Final reply rendered as Markdown after stream completes
- os.getlogin() replaced with os.getenv("USER") for container compatibility

Dockerfile.cli + docker-compose cli service (profiles: tools):
- Run: docker compose --profile tools run --rm -it cli

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

Dockerfile.cli

@@ -0,0 +1,9 @@
+FROM python:3.12-slim
+
+WORKDIR /app
+
+RUN pip install --no-cache-dir rich
+
+COPY cli.py .
+
+CMD ["python3", "cli.py"]