add AI and generation routers, models, and OpenRouter service integration with tests

Co-authored-by: Copilot <copilot@github.com>

backend/app/main.py

@@ -1,6 +1,8 @@
 from backend.app.routers import auth as auth_router
 from backend.app.routers import users as users_router
 from backend.app.routers import admin as admin_router
+from backend.app.routers import ai as ai_router
+from backend.app.routers import generate as generate_router
 from backend.app.db import close_db, init_db
 import os
 from contextlib import asynccontextmanager
@@ -37,6 +39,8 @@ app.add_middleware(
 app.include_router(auth_router.router)
 app.include_router(users_router.router)
 app.include_router(admin_router.router)
+app.include_router(ai_router.router)
+app.include_router(generate_router.router)
 
 
 @app.get("/health", tags=["health"])