Fix run_standalone.py to use venv python for uvicorn

- Script was using /usr/bin/python3 which doesn't have uvicorn installed
- Now detects and uses venv/bin/python3 if available
- Backend now starts correctly with: 'python3 scripts/run_standalone.py start|restart'
- All services (Backend, Frontend, SSL Proxy) now start properly

scripts/run_standalone.py

@@ -120,8 +120,14 @@ def start_backend(backend_port: int, backend_cfg: Dict[str, Any], background: bo
     os.makedirs(env["DATA_DIR"], exist_ok=True)
     os.makedirs(env["LOGS_DIR"], exist_ok=True)
 
+    # Use venv python if available
+    python_exe = sys.executable
+    venv_python = os.path.join(os.path.dirname(os.path.dirname(os.path.abspath(__file__))), "venv", "bin", "python3")
+    if os.path.exists(venv_python):
+        python_exe = venv_python
+
     cmd = [
-        sys.executable, "-m", "uvicorn", 
+        python_exe, "-m", "uvicorn",
         "backend.main:app",
         "--host", "0.0.0.0",
         "--port", str(backend_port)