feat: add Ollama Cloud as built-in provider

Add ollama-cloud as a first-class provider with full parity to existing
API-key providers (gemini, zai, minimax, etc.):

- PROVIDER_REGISTRY entry with OLLAMA_API_KEY env var
- Provider aliases: ollama -> custom (local), ollama_cloud -> ollama-cloud
- models.dev integration for accurate context lengths
- URL-to-provider mapping (ollama.com -> ollama-cloud)
- Passthrough model normalization (preserves Ollama model:tag format)
- Default auxiliary model (nemotron-3-nano:30b)
- HermesOverlay in providers.py
- CLI --provider choices, CANONICAL_PROVIDERS entry
- Dynamic model discovery with disk caching (1hr TTL)
- 37 provider-specific tests

Cherry-picked from PR #6038 by kshitijk4poor. Closes #3926

cli-config.yaml.example

@@ -26,6 +26,7 @@ model:
   #   "huggingface"  - Hugging Face Inference (requires: HF_TOKEN)
   #   "xiaomi"       - Xiaomi MiMo (requires: XIAOMI_API_KEY)
   #   "arcee"        - Arcee AI Trinity models (requires: ARCEEAI_API_KEY)
+  #   "ollama-cloud" - Ollama Cloud (requires: OLLAMA_API_KEY — https://ollama.com/settings)
   #   "kilocode"     - KiloCode gateway (requires: KILOCODE_API_KEY)
   #   "ai-gateway"   - Vercel AI Gateway (requires: AI_GATEWAY_API_KEY)
   #
@@ -37,12 +38,6 @@ model:
   #     base_url: "http://localhost:1234/v1"
   #   No API key needed — local servers typically ignore auth.
   #
-  #   For Ollama Cloud (https://ollama.com/pricing):
-  #     provider: "custom"
-  #     base_url: "https://ollama.com/v1"
-  #   Set OLLAMA_API_KEY in .env — automatically picked up when base_url
-  #   points to ollama.com.
-  #
   # Can also be overridden with --provider flag or HERMES_INFERENCE_PROVIDER env var.
   provider: "auto"
   
@@ -337,6 +332,7 @@ compression:
 #   "openrouter" - Force OpenRouter (requires OPENROUTER_API_KEY)
 #   "nous"       - Force Nous Portal (requires: hermes login)
 #   "gemini"      - Force Google AI Studio direct (requires: GOOGLE_API_KEY or GEMINI_API_KEY)
+#   "ollama-cloud" - Ollama Cloud (requires: OLLAMA_API_KEY)
 #   "codex"       - Force Codex OAuth (requires: hermes model → Codex).
 #                  Uses gpt-5.3-codex which supports vision.
 #   "main"       - Use your custom endpoint (OPENAI_BASE_URL + OPENAI_API_KEY).