feat(ai): provider router (ollama|gemini|groq) for heavy CV calls

The structured /cv/* calls funnel through a provider router so production can
offload a weak local GPU (GTX 1060) to a cloud provider without any .NET change.
Default stays "ollama" (keyless/local) and /summarize remains local distilbart.

- AI_PROVIDER=ollama|gemini|groq dispatch inside _ollama_generate_json/_text
  (entry-point names kept, so no call sites change; Ollama path is byte-identical).
- Gemini (x-goog-api-key header, not URL query) and Groq (OpenAI-compatible
  chat/completions) added via stdlib urllib — zero new dependencies.
- /health reports ai_provider + ai_provider_configured.
- Keys read from env only; never logged/committed.
- Compose + .env.example pass AI_PROVIDER/GEMINI_*/GROQ_* through.

Tests: 11 passed (default Ollama unchanged, Gemini/Groq dispatch, missing-key 503,
health reports provider).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

docker-compose.yml

@@ -74,6 +74,13 @@ services:
     environment:
       - OLLAMA_BASE_URL=${OLLAMA_BASE_URL:-http://ollama:11434}
       - OLLAMA_MODEL=${OLLAMA_MODEL:-qwen2.5:7b}
+      # AI provider for heavy /cv/* calls: ollama (default) | gemini | groq.
+      # Set AI_PROVIDER=gemini + GEMINI_API_KEY in prod to offload a weak local GPU.
+      - AI_PROVIDER=${AI_PROVIDER:-ollama}
+      - GEMINI_API_KEY=${GEMINI_API_KEY:-}
+      - GEMINI_MODEL=${GEMINI_MODEL:-gemini-2.0-flash}
+      - GROQ_API_KEY=${GROQ_API_KEY:-}
+      - GROQ_MODEL=${GROQ_MODEL:-llama-3.3-70b-versatile}
     ports:
       - "8001:8001"
     depends_on: