ifcmcp: fail early with clear message when mcp package is not installed

mcp is an optional dependency so that the embedded API (embedded.py) can
be used from Pyodide without pulling in pydantic-core and the rest of the
MCP protocol stack, which may not be available in all WASM environments.

src/ifcmcp/ifcmcp/__main__.py

@@ -27,6 +27,17 @@ def main():
 
     args = parser.parse_args()
 
+    try:
+        from mcp.server.fastmcp import FastMCP  # noqa: F401
+    except ImportError:
+        import sys
+        print(
+            "error: the 'mcp' package is required to run the server.\n"
+            "Install it with:  pip install mcp",
+            file=sys.stderr,
+        )
+        sys.exit(1)
+
     from ifcmcp.server import build_server
 
     server = build_server()