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/routers/local_llm.py

@@ -54,7 +54,10 @@ def _render(username: str, success: str = "", error: str = "") -> str:
     # ── Host rows ─────────────────────────────────────────────────────────────
     host_rows = ""
     for h in hosts:
-        key_hint = f"…{h['api_key'][-4:]}" if h.get("api_key") else "not set"
+        key_hint  = f"…{h['api_key'][-4:]}" if h.get("api_key") else "not set"
+        ht        = h.get("host_type", "openwebui")
+        ow_sel    = ' selected' if ht == "openwebui" else ''
+        ai_sel    = ' selected' if ht == "openai"    else ''
         host_rows += f'''
         <div class="host-row">
           <form method="POST" action="/settings/local/host" class="host-form">
@@ -72,11 +75,20 @@ def _render(username: str, success: str = "", error: str = "") -> str:
                        autocomplete="off" spellcheck="false" data-form-type="other">
               </div>
             </div>
-            <div class="field">
-              <label>API Key</label>
-              <input type="password" name="api_key" placeholder="Leave blank to keep existing"
-                     autocomplete="new-password" data-1p-ignore data-lpignore="true" data-form-type="other">
-              <p class="key-status">Current: {key_hint}</p>
+            <div class="field-row">
+              <div class="field">
+                <label>API Key</label>
+                <input type="password" name="api_key" placeholder="Leave blank to keep existing"
+                       autocomplete="new-password" data-1p-ignore data-lpignore="true" data-form-type="other">
+                <p class="key-status">Current: {key_hint}</p>
+              </div>
+              <div class="field" style="flex:0 0 auto">
+                <label>Type</label>
+                <select name="host_type">
+                  <option value="openwebui"{ow_sel}>Open WebUI / Ollama</option>
+                  <option value="openai"{ai_sel}>OpenAI-compatible (OpenRouter, etc.)</option>
+                </select>
+              </div>
             </div>
             <div class="btn-row">
               <button type="submit" class="btn btn-secondary btn-sm">Save host</button>
@@ -197,19 +209,20 @@ async def models_page(request: Request):
 
 @router.post("/settings/local/host", include_in_schema=False)
 async def save_host(
-    request: Request,
-    host_id:  str = Form(""),
-    label:    str = Form(""),
-    api_url:  str = Form(""),
-    api_key:  str = Form(""),
+    request:   Request,
+    host_id:   str = Form(""),
+    label:     str = Form(""),
+    api_url:   str = Form(""),
+    api_key:   str = Form(""),
+    host_type: str = Form("openwebui"),
 ):
     username = _get_user(request)
     if not username:
         return RedirectResponse("/login", status_code=302)
     if not api_url.strip():
         return HTMLResponse(_render(username, error="API URL is required."))
-    reg.save_host(username, host_id or None, label, api_url, api_key)
-    logger.info("model registry host saved: %s", username)
+    reg.save_host(username, host_id or None, label, api_url, api_key, host_type)
+    logger.info("model registry host saved: %s (%s)", username, host_type)
     return HTMLResponse(_render(username, success="Host saved."))
 
 
@@ -306,8 +319,10 @@ async def fetch_models(request: Request, host_id: str = "") -> JSONResponse:
     if not api_url:
         return JSONResponse({"error": "No host configured."}, status_code=400)
 
-    url     = api_url.rstrip("/") + "/api/models"
-    headers = {"Authorization": f"Bearer {api_key}"} if api_key else {}
+    host_type   = host.get("host_type", "openwebui") if host else "openwebui"
+    models_path = "/models" if host_type == "openai" else "/api/models"
+    url         = api_url.rstrip("/") + models_path
+    headers     = {"Authorization": f"Bearer {api_key}"} if api_key else {}
 
     try:
         async with httpx.AsyncClient(timeout=8) as client: