feat: host_type field for OpenRouter / OpenAI-compatible API support

Adds host_type ("openwebui" | "openai") to the host schema so Cortex can
talk to both Open WebUI/Ollama and OpenRouter/standard-OpenAI endpoints.

Path differences per type:
  openwebui (default): /api/chat/completions, /api/models
  openai:              /chat/completions,     /models

model_registry.py:
  - host_type added to host schema (default "openwebui", backward compat)
  - save_host() accepts host_type parameter
  - _resolve_model() passes host_type through with the merged host fields

llm_client._local():
  - Reads host_type from resolved model_cfg
  - Selects correct chat completions path accordingly

routers/local_llm.py:
  - save_host route accepts host_type form field
  - fetch-models uses /models for openai type, /api/models for openwebui
  - Existing host rows show type selector pre-filled from stored value

local_llm.html:
  - "Add host" form includes type selector

To use OpenRouter:
  - Add host: URL = https://openrouter.ai/api/v1, Type = OpenAI-compatible
  - API key from openrouter.ai (store in .env or model_registry.json only)
  - Fetch models or add manually (e.g. anthropic/claude-sonnet-4-5-20251022)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

cortex/model_registry.py

@@ -6,7 +6,18 @@ Stored in: home/{user}/model_registry.json
 Schema:
   {
     "version": 1,
-    "hosts": [{"id", "label", "api_url", "api_key"}, ...],
+    "hosts": [{"id", "label", "api_url", "api_key",
+               "host_type": "openwebui" | "openai"}, ...],
+    #
+    # host_type controls the API path layout:
+    #   "openwebui"  (default) — Open WebUI / Ollama:
+    #                   chat:   POST {url}/api/chat/completions
+    #                   models: GET  {url}/api/models
+    #   "openai"     — OpenRouter, LiteLLM, Anthropic-compatible, etc.:
+    #                   chat:   POST {url}/chat/completions
+    #                   models: GET  {url}/models
+    #   Set api_url to the base path that ends just before /chat/completions,
+    #   e.g. https://openrouter.ai/api/v1  for OpenRouter.
     "models": [
       {
         "id":         str,             # unique within this registry
@@ -212,7 +223,12 @@ def _resolve_model(registry: dict, model_id: str) -> dict | None:
         if not host:
             logger.warning("model %s references missing host_id %s", model_id, host_id)
             return None
-        return {**model, "api_url": host.get("api_url", ""), "api_key": host.get("api_key", "")}
+        return {
+            **model,
+            "api_url":   host.get("api_url", ""),
+            "api_key":   host.get("api_key", ""),
+            "host_type": host.get("host_type", "openwebui"),
+        }
 
     return dict(model)
 
@@ -308,15 +324,21 @@ def get_defined_roles(username: str) -> dict[str, dict]:
 # ── Write API (CRUD) ──────────────────────────────────────────────────────────
 
 def save_host(username: str, host_id: str | None,
-              label: str, api_url: str, api_key: str) -> str:
-    """Create or update a host. Returns the host ID."""
+              label: str, api_url: str, api_key: str,
+              host_type: str = "openwebui") -> str:
+    """Create or update a host. Returns the host ID.
+
+    host_type: "openwebui" (default) or "openai" (OpenRouter, LiteLLM, etc.)
+    """
     data = _load(username)
+    host_type = host_type if host_type in ("openwebui", "openai") else "openwebui"
 
     if host_id:
         for h in data["hosts"]:
             if h["id"] == host_id:
-                h["label"]   = label.strip()
-                h["api_url"] = api_url.strip()
+                h["label"]     = label.strip()
+                h["api_url"]   = api_url.strip()
+                h["host_type"] = host_type
                 if api_key.strip():
                     h["api_key"] = api_key.strip()
                 _save(username, data)
@@ -325,10 +347,11 @@ def save_host(username: str, host_id: str | None,
 
     host_id = secrets.token_hex(4)
     data["hosts"].append({
-        "id":      host_id,
-        "label":   label.strip(),
-        "api_url": api_url.strip(),
-        "api_key": api_key.strip(),
+        "id":        host_id,
+        "label":     label.strip(),
+        "api_url":   api_url.strip(),
+        "api_key":   api_key.strip(),
+        "host_type": host_type,
     })
     _save(username, data)
     return host_id