Fix remaining lint errors on main

- mypy: django-stubs 6.0.3 still flagged validate_v3_migration.py after
  PR #1367's `.values_list(...)` refactor because calling `.values_list()`
  on an annotated ValuesQuerySet types the result as the annotated model,
  not a tuple iterable. Materialise the slice via `cast(list[tuple[...]],
  list(...))` so the for-loop destructures a concrete tuple.

- prettier: `public/env-config.js` is a gitignored artefact produced by
  `env.sh` at container start. It was tripping `yarn lint` locally even
  though it never exists in CI. Add it to .prettierignore so the ignore
  surface matches .gitignore.

Verified by running `pre-commit run --all-files` (all hooks pass) and
`yarn lint` in frontend/ (prettier clean).

Author: JSv4

frontend/.prettierignore

@@ -13,6 +13,7 @@ node_modules/
 # Generated files
 *.min.js
 *.min.css
+public/env-config.js
 
 # Playwright cache
 playwright/.cache/

opencontractserver/documents/management/commands/validate_v3_migration.py

@@ -9,6 +9,7 @@
 """
 
 import logging
+from typing import cast
 
 from django.core.management.base import BaseCommand
 from django.db.models import Count
@@ -298,9 +299,14 @@ def _check_structural_set_uniqueness(self, verbose):
         )
 
         if verbose:
-            for content_hash, count in duplicates.values_list(
-                "content_hash", "count"
-            )[:5]:
+            # django-stubs 6.0.3 mistypes `.values().annotate().values_list()`
+            # chains as the annotated model rather than a tuple iterable, so
+            # materialise with an explicit cast. Functionally identical.
+            top_duplicates = cast(
+                list[tuple[str, int]],
+                list(duplicates.values_list("content_hash", "count")[:5]),
+            )
+            for content_hash, count in top_duplicates:
                 self.stdout.write(
                     f"    - Hash {content_hash[:16]}...: {count} duplicates"
                 )