Add job processing system with streaming endpoint

Introduced a `processing` router to handle job streaming using server-sent events. Added `Jobs` and `JobStatus` models for managing job-related data, along with database creation logic. Updated the `sample` router to create new job entries during experiment creation.

backend/app/routers/processing.py

@@ -0,0 +1,24 @@
+from fastapi import APIRouter, Depends
+from sqlalchemy.orm import Session
+from starlette.responses import StreamingResponse
+import asyncio
+import json
+
+from app.models import JobStatus, Jobs as JobModel
+from app.dependencies import get_db
+
+router = APIRouter()
+
+
+async def job_event_generator(db):
+    while True:
+        jobs = db.query(JobModel).filter(JobModel.status == JobStatus.TODO).all()
+
+        if jobs:
+            yield json.dumps([job.parameters for job in jobs]) + "\n\n"
+        await asyncio.sleep(5)
+
+
+@router.get("/jobs/stream")
+async def stream_jobs(db: Session = Depends(get_db)):
+    return StreamingResponse(job_event_generator(db), media_type="text/event-stream")