Fix Gradio 5.x: move respond, build_messages, chat_with_backend to module level

Fix /respond endpoint: add api_key and model_select to button click handlers

Fix Gradio 5.x compatibility: remove .update() calls on Plot components

Fix gr.Plot: remove interactive=False (Gradio 5.x incompatible)

Fix sdk_version: 5.49.1 to match requirements.txt

Fix colorTo: use purple instead of violet (HF Spaces validation)

Initial CAPT Explorer deployment - interactive cognitive architecture demo

initial commit