Use persistent storage for database

Default DB_PATH to /data/ so annotations survive Space restarts.

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

app.py

@@ -16,7 +16,7 @@ from pathlib import Path
 from flask import Flask, Response, jsonify, redirect, request, send_file, session
 
 DATASET_PATH = Path(os.environ.get("DATASET_PATH", "evaluation_dataset.jsonl"))
-DB_PATH = Path(os.environ.get("DB_PATH", "annotations.db"))
+DB_PATH = Path(os.environ.get("DB_PATH", "/data/annotations.db"))
 
 ANNOTATION_FIELDS = (
     "bewertung", "korrekt", "relevant", "vollstaendig", "kohaerenz", "anmerkungen",