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>

tests/use_cases/cli_startup.md

@@ -1,13 +1,13 @@
 # Use Case: CLI Startup
 
-Verify the Adolf CLI starts cleanly and exits without error when the user closes input.
+Verify the Adolf CLI container starts cleanly, shows the welcome banner,
+and exits without error when the user closes input.
 
 ## Steps
 
-Run the CLI with empty stdin (simulates user pressing Ctrl+D immediately):
-
 ```bash
-echo "" | python3 /home/alvis/adolf/cli.py --session use-case-cli-startup
+echo "" | docker compose --profile tools run --rm -T cli \
+  python3 cli.py --url http://deepagents:8000 --session use-case-cli-startup
 echo "exit code: $?"
 ```