feat: implement skeleton phase

examples/config.py

@@ -0,0 +1,18 @@
+# Stub user config for the Phase 0 DoD.
+#
+# Loader (beaver_gateway/config_loader.py) execs this file with
+# ClaudeAgent, RaycastAgent, McpServer, ExposedMcp, Gateway already
+# bound. The top-level `gateway = Gateway(...)` is what gets picked up.
+
+gateway = Gateway(  # type: ignore[name-defined]  # noqa: F821
+    agents=[
+        ClaudeAgent(  # type: ignore[name-defined]  # noqa: F821
+            name="stub",
+            model="claude-sonnet-4-5",
+            system_prompt="You are a stub agent used to validate the Phase 0 skeleton.",
+            cwd="/tmp",
+        ),
+    ],
+    mcps=[],
+    frontends=[],
+)