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

hermes_cli/config.py

@@ -1024,6 +1024,22 @@ OPTIONAL_ENV_VARS = {
         "category": "provider",
         "advanced": True,
     },
+    "OLLAMA_API_KEY": {
+        "description": "Ollama Cloud API key (ollama.com — cloud-hosted open models)",
+        "prompt": "Ollama Cloud API key",
+        "url": "https://ollama.com/settings",
+        "password": True,
+        "category": "provider",
+        "advanced": True,
+    },
+    "OLLAMA_BASE_URL": {
+        "description": "Ollama Cloud base URL override (default: https://ollama.com/v1)",
+        "prompt": "Ollama base URL (leave empty for default)",
+        "url": None,
+        "password": False,
+        "category": "provider",
+        "advanced": True,
+    },
     "XIAOMI_API_KEY": {
         "description": "Xiaomi MiMo API key for MiMo models (mimo-v2-pro, mimo-v2-omni, mimo-v2-flash)",
         "prompt": "Xiaomi MiMo API Key",