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/providers.py

@@ -141,6 +141,10 @@ HERMES_OVERLAYS: Dict[str, HermesOverlay] = {
         base_url_override="https://api.arcee.ai/api/v1",
         base_url_env_var="ARCEE_BASE_URL",
     ),
+    "ollama-cloud": HermesOverlay(
+        transport="openai_chat",
+        base_url_env_var="OLLAMA_BASE_URL",
+    ),
 }
 
 
@@ -250,7 +254,7 @@ ALIASES: Dict[str, str] = {
     "lmstudio": "lmstudio",
     "lm-studio": "lmstudio",
     "lm_studio": "lmstudio",
-    "ollama": "ollama-cloud",
+    "ollama": "custom",  # bare "ollama" = local; use "ollama-cloud" for cloud
     "vllm": "local",
     "llamacpp": "local",
     "llama.cpp": "local",
@@ -269,6 +273,7 @@ _LABEL_OVERRIDES: Dict[str, str] = {
     "xiaomi": "Xiaomi MiMo",
     "local": "Local endpoint",
     "bedrock": "AWS Bedrock",
+    "ollama-cloud": "Ollama Cloud",
 }