Add autocomplete suggestions for Author, Chapter, and Reviewer fields

Adds a GET /api/jobs/suggestions endpoint that returns distinct values for
author, chapter, and reviewer_name from the database, and wires them into
HTML datalist elements on the New Job, result view, and Browse Jobs pages.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/main.py

@@ -754,6 +754,31 @@ async def list_jobs(
     return JSONResponse({"total": total, "limit": limit, "offset": offset, "jobs": rows})
 
 
+@app.get("/api/jobs/suggestions")
+async def job_suggestions():
+    """Return distinct values for author, chapter, and reviewer_name to power autocomplete."""
+    try:
+        with get_db() as conn:
+            with conn.cursor() as cur:
+                cur.execute("""
+                    SELECT
+                        array_remove(array_agg(DISTINCT author ORDER BY author), NULL) AS authors,
+                        array_remove(array_agg(DISTINCT chapter ORDER BY chapter), NULL) AS chapters,
+                        array_remove(array_agg(DISTINCT reviewer_name ORDER BY reviewer_name), NULL) AS reviewers
+                    FROM ocr_jobs
+                """)
+                row = cur.fetchone()
+    except Exception as exc:
+        print(f"suggestions DB error: {exc}")
+        raise HTTPException(status_code=500, detail="Database error.")
+
+    return JSONResponse({
+        "authors": row["authors"] or [],
+        "chapters": row["chapters"] or [],
+        "reviewers": row["reviewers"] or [],
+    })
+
+
 @app.get("/api/jobs/{job_id}")
 async def get_job(job_id: str):
     """Retrieve full job record including OCR text."""