Migrate Open WebUI and coding CLIs to the AI proxy (resolves #15)

Open WebUI now points at litellm instead of llama-server directly, using a
provisioned virtual key. llama-server's host port is dropped (internal-only
on the ai-stack network) since the proxy is the only intended entry point
now. docs/coding-cli-setup.md repointed at the proxy's endpoints/ports with
per-CLI virtual keys instead of the old shared dummy key.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

.env.example

@@ -12,9 +12,9 @@ LLAMA_PORT=8080
 
 # --- Open WebUI ---
 WEBUI_PORT=3000
-# Dummy key — llama.cpp's OpenAI-compatible endpoint doesn't check it, but
-# Open WebUI requires the field to be non-empty.
-OPENAI_API_KEY=local
+# Required — create an "openwebui" virtual key in LiteLLM's Admin UI first
+# (see docs/proxy-key-onboarding.md), then paste it here.
+OPENWEBUI_LITELLM_KEY=
 
 # --- Lazytainer ---
 # Seconds of inactivity before llama-server is stopped. 900 = 15 min.