fix: use environment variable for FastMCP stateless_http mode

Use FASTMCP_STATELESS_HTTP env var instead of constructor parameter
to avoid deprecation warning in FastMCP >= 2.x.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: MarkusNeusinger

api/mcp/server.py

@@ -64,9 +64,12 @@ async def get_mcp_db_session() -> AsyncSession:
     return _mcp_session_factory()
 
 
+# Enable stateless HTTP mode via environment variable (recommended approach)
+# This allows horizontal scaling without session affinity
+os.environ.setdefault("FASTMCP_STATELESS_HTTP", "true")
+
 # Initialize FastMCP server
-# stateless_http=True allows horizontal scaling without session affinity
-mcp_server = FastMCP("pyplots", stateless_http=True)
+mcp_server = FastMCP("pyplots")
 
 
 @mcp_server.tool()