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

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,