feat: add jobs CRUD API with manual execution

- Full CRUD for backup jobs
- Manual job trigger endpoint with background execution
- Schedule creation endpoint
- Tests for job creation, update, execution, and 404 cases

backend/app/main.py

@@ -0,0 +1,15 @@
+from fastapi import FastAPI
+from contextlib import asynccontextmanager
+from app.database import engine, Base
+from app.routers import sources, jobs
+
+@asynccontextmanager
+async def lifespan(app: FastAPI):
+    async with engine.begin() as conn:
+        await conn.run_sync(Base.metadata.create_all)
+    yield
+
+app = FastAPI(title="Backup Tool API", lifespan=lifespan)
+
+app.include_router(sources.router)
+app.include_router(jobs.router)