fix: auto-append /chat/completions to base URL

The CU Cloud gateway base URL is /v1 but the actual endpoint needs
/chat/completions appended. Auto-detect and append when missing.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

ai_review/llm.py

@@ -150,7 +150,10 @@ def call_llm(system_msg, user_msg, max_tokens=4096, timeout=300, model=None, ena
         "Authorization": f"Bearer {API_KEY}"
     }
     data = json.dumps(payload).encode("utf-8")
-    req = urllib.request.Request(API_URL, data=data, headers=headers, method="POST")
+    url = API_URL.rstrip("/")
+    if not url.endswith("/chat/completions"):
+        url = url + "/chat/completions"
+    req = urllib.request.Request(url, data=data, headers=headers, method="POST")
 
     try:
         with urllib.request.urlopen(req, timeout=timeout) as resp: