docs(noxa-9fw.4): describe gemini cli as primary llm backend

- Update CLAUDE.md: provider chain, LLM modules section, CLI examples
- Update env.example: add GEMINI_MODEL, reorder providers (Gemini first)
- Update noxa-llm/src/lib.rs crate doc comment

env.example

@@ -5,7 +5,10 @@
 
 # --- LLM Providers ---
 
-# Ollama (local, default provider)
+# Gemini CLI (primary provider — requires `gemini` binary on PATH)
+# GEMINI_MODEL=gemini-2.5-pro   # defaults to gemini-2.5-pro
+
+# Ollama (fallback; local inference)
 OLLAMA_HOST=http://localhost:11434
 OLLAMA_MODEL=qwen3:8b