fix(6): add missing Toast component and fix backend startup

- Create Toast component for success/error messages
- Fix uvicorn invocation: use backend.main:app from project root
- Ensures relative imports work correctly in backend modules

frontend/components/Toast.tsx

@@ -0,0 +1,34 @@
+'use client';
+
+import { useEffect } from 'react';
+
+export interface ToastProps {
+  type: 'success' | 'error' | 'warning' | 'info';
+  message: string;
+  onClose: () => void;
+  duration?: number;
+}
+
+export function Toast({ type, message, onClose, duration = 3000 }: ToastProps) {
+  useEffect(() => {
+    const timer = setTimeout(onClose, duration);
+    return () => clearTimeout(timer);
+  }, [onClose, duration]);
+
+  const bgColor = {
+    success: 'bg-green-500',
+    error: 'bg-red-500',
+    warning: 'bg-yellow-500',
+    info: 'bg-blue-500',
+  }[type];
+
+  return (
+    <div
+      className={`fixed bottom-4 right-4 ${bgColor} text-white px-4 py-2 rounded shadow-lg z-50 animate-fade-in`}
+      role="alert"
+      aria-live="polite"
+    >
+      {message}
+    </div>
+  );
+}

start_servers.py

@@ -120,27 +120,26 @@ class StandaloneServerManager:
             )
 
     def start_backend(self):
-        """Start FastAPI backend server using uvicorn directly from project root"""
+        """Start FastAPI backend server using uvicorn from project root"""
         self.log(f"Starting backend on port {self.backend_port}...")
         backend_log = self.logs_dir / "backend.log"
-        backend_dir = self.root_dir / "backend"
 
         env = os.environ.copy()
         env['PATH'] = f"{self.python_exe.parent}:{env['PATH']}"
 
-        # Use uvicorn CLI from venv to run the app
+        # Use uvicorn CLI from project root with full module path (backend.main:app)
         with open(backend_log, 'w') as log_f:
             self.backend_process = subprocess.Popen(
                 [
                     str(self.python_exe),
                     "-m",
                     "uvicorn",
-                    "main:app",
+                    "backend.main:app",
                     "--host", "0.0.0.0",
                     "--port", str(self.backend_port),
                     "--log-level", self.log_level
                 ],
-                cwd=str(backend_dir),
+                cwd=str(self.root_dir),
                 stdout=log_f,
                 stderr=subprocess.STDOUT,
                 env=env,