feat(jobs): add background job support for benchmarks and processing

Why:
- Long benchmark and process runs block HTTP clients; task #20 required async execution.

Changes:
- SQLite jobs table + GET /jobs and GET /jobs/{id}
- POST /benchmarks?background=true and POST /documents/{id}/process?background=true return 202 + job_id
- FastAPI BackgroundTasks execute work in-process; sync paths unchanged

Impact:
- Jobs are lost on server restart (Option A, no external queue)

Co-authored-by: Cursor <cursoragent@cursor.com>

src/documents/routes.py

@@ -2,12 +2,13 @@
 
 Endpoints:
   POST   /documents              Upload a .docx / .doc / .pdf file
-  POST   /documents/{id}/process  Run chunking strategies
+  POST   /documents/{id}/process  Run chunking strategies; ?background=true enqueues a job
   DELETE /documents/{id}          Remove document + vectors
   GET    /strategies              List available chunking strategies
 """
 
-from fastapi import APIRouter, File, UploadFile
+from fastapi import APIRouter, BackgroundTasks, File, Query, UploadFile
+from fastapi.responses import JSONResponse
 
 from src.core.exceptions import DocumentProcessingError
 from src.documents.models import (
@@ -21,6 +22,9 @@ from src.documents.models import (
 )
 from src.documents.parser import SUPPORTED_SUFFIXES
 from src.documents import service
+from src.jobs import service as jobs_service
+from src.jobs.models import JobCreatedResponse
+from src.storage import sqlite as db
 
 router = APIRouter()
 
@@ -63,9 +67,32 @@ async def upload_document(file: UploadFile = File(...)):
     )
 
 
-@router.post("/documents/{doc_id}/process", response_model=ProcessResponse)
-async def process_document(doc_id: str, request: ProcessRequest):
-    """Run selected chunking strategies on an uploaded document."""
+@router.post("/documents/{doc_id}/process")
+async def process_document(
+    doc_id: str,
+    request: ProcessRequest,
+    background_tasks: BackgroundTasks,
+    background: bool = Query(
+        False, description="Run in background; returns job_id (HTTP 202)"
+    ),
+):
+    """Run selected chunking strategies on an uploaded document.
+
+    Pass ``background=true`` to enqueue and poll ``GET /jobs/{job_id}``.
+    """
+    if background:
+        if db.get_document(doc_id) is None:
+            raise DocumentProcessingError(f"Document not found: {doc_id}")
+        job = jobs_service.enqueue_process(doc_id, request)
+        background_tasks.add_task(jobs_service.run_process_job, job["id"])
+        body = JobCreatedResponse(
+            job_id=job["id"],
+            job_type=job["job_type"],
+            status=job["status"],
+            poll_url=f"/jobs/{job['id']}",
+        )
+        return JSONResponse(status_code=202, content=body.model_dump())
+
     return service.process_document(doc_id, request)