Add React frontend and Sinbad2IA LLM integration.

Introduce a full Vite/React UI for exams, auth, materials, images, generation, and export.
Adapt backend for Sinbad2IA chat API, bcrypt passwords, CORS on port 5173, and schema migrations.

backend/app/core/config.py

@@ -10,14 +10,14 @@ class Settings(BaseSettings):
     api_prefix: str = ""
     api_key: str = Field(min_length=16)
     database_url: str = "postgresql+psycopg://genexamenes:genexamenes@localhost:5432/genexamenes"
-    allowed_origins: str = "http://localhost:3000"
+    allowed_origins: str = "http://localhost:5173,http://localhost:3000"
     rate_limit_requests: int = Field(default=60, ge=1)
     rate_limit_window_seconds: int = Field(default=60, ge=1)
     max_request_bytes: int = Field(default=1_048_576, ge=1_024)
     llm_api_key: str | None = None
-    llm_base_url: str = "https://api.openai.com/v1"
-    llm_model: str = "gpt-4o-mini"
-    llm_timeout_seconds: int = Field(default=60, ge=5)
+    llm_base_url: str = ""
+    llm_model: str = "qwen3.5:35b"
+    llm_timeout_seconds: int = Field(default=180, ge=5)
     jwt_secret_key: str = Field(min_length=32)
     jwt_algorithm: str = "HS256"
     jwt_expire_minutes: int = Field(default=60 * 24, ge=5)

backend/app/core/middleware.py

@@ -17,6 +17,9 @@ class RateLimitMiddleware(BaseHTTPMiddleware):
         self.requests: defaultdict[str, deque[float]] = defaultdict(deque)
 
     async def dispatch(self, request: Request, call_next: RequestResponseEndpoint) -> Response:
+        if request.method == "OPTIONS":
+            return await call_next(request)
+
         client = request.client.host if request.client else "unknown"
         now = time.monotonic()
         bucket = self.requests[client]