Let a maintenance script find the database the site actually uses

Running `python scripts/export_catalog.py` on a deployed site died with
1045 "Access denied for user 'root'@'localhost'", naming a user that site
does not have.

Nothing loads .env for a plain script run. wsgi.py calls load_dotenv() for the
served app and the flask CLI loads .env for itself, so both reach the real
database; a bare `python scripts/...` gets neither. DATABASE_URL then stays
unset, FLASK_ENV defaults to development, and config.py falls back to a
hardcoded root@localhost URL.

The read-only failure above is the harmless version. Six of these seven
scripts WRITE - backfill, reclassify, retype, collapse, refile, import - and
on any box where those fallback root credentials happen to resolve, they would
have silently rewritten the wrong database with no error at all. That is also
why this survived: the dev .env points at root, so the fallback matched what
the developer expected and nothing ever looked wrong here.

All seven now load .env from the repo root, resolved from __file__ rather than
the working directory, since these are run by hand during a deployment and
rarely from the repo root.

tests/test_maintenance_scripts.py pins it for any future script: every script
that calls create_app must call load_dotenv, before create_app rather than
after it, and with an explicit path rather than a cwd-relative search.

scripts/collapse_duplicate_backup_revisions.py

@@ -38,11 +38,24 @@ database backup before --commit anyway; this deletes rows.
 import argparse
 import os
 import sys
+from pathlib import Path
 from collections import defaultdict
 
 # Run from anywhere: put the repo root (parent of scripts/) on the path.
 sys.path.insert(0, os.path.dirname(os.path.dirname(os.path.abspath(__file__))))
 
+from dotenv import load_dotenv
+
+# Load .env before anything reads config. wsgi.py does this for the served app
+# and the `flask` CLI does it for itself, but a plain `python scripts/...` run
+# gets neither: DATABASE_URL stays unset, FLASK_ENV defaults to development,
+# and config falls back to a hardcoded root@localhost URL. That fails on a real
+# deployment with a bare 1045 Access denied for 'root', naming a user the site
+# does not use - and on a box where those root credentials happen to work, it
+# is worse, because the script silently reads or WRITES the wrong database.
+load_dotenv(Path(__file__).resolve().parent.parent / '.env')
+
+
 from shopdb import create_app
 from shopdb.api import db
 from shopdb.core.models import Asset