feat: add /health endpoint bypassing transport security

- Migrate from SSE to HTTP transport using fastmcp>=2.0
- Add /health endpoint for Docker health checks and load balancers
- Remove MCP_ALLOWED_HOSTS (no longer needed with http_app approach)
- Add lifespan handler for proper task group initialization
- Install curl in Docker image for health checks
- Update Makefile with test-health and test-mcp targets
- Update documentation to reflect new endpoint structure

Fixes: Health check fails with 421 Misdirected Request when
MCP_ALLOWED_HOSTS doesn't include localhost

Dockerfile

@@ -19,6 +19,10 @@ FROM python:3.11-slim-bullseye
 
 WORKDIR /app
 
+# Install curl for health checks
+RUN apt-get update && apt-get install -y --no-install-recommends curl \
+    && rm -rf /var/lib/apt/lists/*
+
 # Copy installed dependencies from builder
 # We copy the entire site-packages directory
 COPY --from=builder /usr/local/lib/python3.11/site-packages/ /usr/local/lib/python3.11/site-packages/