Add abuse mitigation: 10 msg/min, 50 msg/session, 2000 char limit, 5000 daily global cap

Fix: upgrade to gradio 5.6 (resolves HfFolder import + audioop)

Fix: Python 3.11 pin (audioop), correct AIGENCY API protocol, session chat_id, image flow

Initial release — interactive AIGENCY V4 demo (Gradio)