fix: agent Dockerfile package structure and Dead container crash

- Dockerfile: COPY to /app/agent/ and use agent.main:app for proper
  package imports
- docker_ops: use low-level API in get_health() to avoid NotFound on
  containers stuck in Docker Dead state
- Add comprehensive README with architecture, API docs, and usage

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

agent/Dockerfile

@@ -7,8 +7,8 @@ RUN apt-get update && apt-get install -y --no-install-recommends curl && rm -rf
 COPY requirements.txt .
 RUN pip install --no-cache-dir -r requirements.txt
 
-COPY . .
+COPY . /app/agent/
 
 EXPOSE 8889
 
-CMD ["uvicorn", "main:app", "--host", "0.0.0.0", "--port", "8889"]
+CMD ["uvicorn", "agent.main:app", "--host", "0.0.0.0", "--port", "8889"]