chore: remove gng, move demo out of lib init

examples/demo.py

@@ -0,0 +1,17 @@
+from pathlib import Path
+
+from agentmsgs.core.app import App
+from agentmsgs.stores.sqlite import SQLiteStore
+
+
+def main():
+    app = App(store=SQLiteStore(Path.home() / ".agentmsgs.db"))
+    alice = app.get_or_create_agent("Alice")
+    bob = app.get_or_create_agent("Bob")
+    t = app.create_thread(alice, bob)
+    app.append(t.id, alice, "Hello")
+    print(app.poll(t.id, bob))
+
+
+if __name__ == "__main__":
+    main()