feat(ops): add backup-db.sh for safe sqlite snapshots

Uses sqlite3.Connection.backup for an online, WAL-safe copy. Resolves
the DB path from QUARTERMASTER_DB_URL or ./quartermaster.db, places
the snapshot in <db-dir>/backups (override with QUARTERMASTER_BACKUP_DIR),
timestamps the filename, and tags it with an optional reason slug.
Absent DB file is a soft exit so the script is safe to call from hooks.

Refs #5

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

.gitignore

@@ -65,6 +65,7 @@ quartermaster.db
 quartermaster.db-journal
 *.sqlite
 *.sqlite3
+backups/
 
 # Flask stuff:
 instance/

scripts/backup-db.sh

@@ -0,0 +1,75 @@
+#!/usr/bin/env bash
+#
+# Copy the quartermaster SQLite database into backups/ before any schema
+# change, data migration, or destructive operation. Safe to run while the
+# application is writing to the DB: uses Python's sqlite3.Connection.backup
+# (the online backup API), not a plain file copy.
+#
+# Usage:
+#   scripts/backup-db.sh [reason]
+#
+# `reason` becomes part of the backup filename. Defaults to "manual".
+#
+# Resolves the database path in this order:
+#   1. QUARTERMASTER_DB_URL if it starts with sqlite:/// (uses the path part)
+#   2. ./quartermaster.db relative to the repo root
+#
+# Exit status:
+#   0  backup written, or source DB does not exist (nothing to do)
+#   1  backup failed, or a non-file sqlite URL was supplied
+
+set -euo pipefail
+
+repo_root="$(cd "$(dirname "${BASH_SOURCE[0]}")/.." && pwd)"
+cd "$repo_root"
+
+reason="${1:-manual}"
+
+exec python3 - "$reason" <<'PY'
+import os
+import re
+import sqlite3
+import sys
+from datetime import datetime
+from pathlib import Path
+
+reason = sys.argv[1]
+
+db_path = Path("quartermaster.db")
+url = os.environ.get("QUARTERMASTER_DB_URL")
+if url:
+    if url.startswith("sqlite:///"):
+        db_path = Path(url[len("sqlite:///"):])
+    elif url.startswith("sqlite://"):
+        print(f"backup-db.sh: non-file sqlite URL not supported: {url}", file=sys.stderr)
+        sys.exit(1)
+    else:
+        print(f"backup-db.sh: QUARTERMASTER_DB_URL is not a sqlite URL: {url}", file=sys.stderr)
+        sys.exit(1)
+
+if not db_path.is_file():
+    print(f"backup-db.sh: no database at {db_path}, nothing to back up.")
+    sys.exit(0)
+
+slug = re.sub(r"[^A-Za-z0-9]+", "-", reason).strip("-") or "manual"
+timestamp = datetime.now().strftime("%Y%m%d-%H%M%S")
+backup_root = os.environ.get("QUARTERMASTER_BACKUP_DIR")
+if backup_root:
+    dest_dir = Path(backup_root)
+else:
+    dest_dir = db_path.resolve().parent / "backups"
+dest_dir.mkdir(parents=True, exist_ok=True)
+dest = dest_dir / f"quartermaster-{timestamp}-{slug}.db"
+
+src = sqlite3.connect(str(db_path))
+try:
+    dst = sqlite3.connect(str(dest))
+    try:
+        src.backup(dst)
+    finally:
+        dst.close()
+finally:
+    src.close()
+
+print(f"backup-db.sh: {db_path} -> {dest} ({dest.stat().st_size} bytes)")
+PY