Phase 3 : hardening qualite de code - typage strict, securite, dead code, a11y

Config strictement stricte partout (ruff, mypy --strict, bandit, vulture,
import-linter, eslint, stylelint), aucune regle desactivee "pour ne pas
casser le build" - l'existant a ete corrige pour la satisfaire plutot que
l'inverse. Hooks pre-commit locaux (language: system) bloquants.

- Typage mypy --strict propage a tout le moteur (db, screens, auth, core,
  ai, routes, puis publish/scripts/tests/app.py/build_css.py).
- Securite : fuite de handle fichier Windows corrigee dans l'export SCORM
  (routes/publish/export_scorm.py), CSRF/RNG non-crypto/xAPI documentes
  (# nosec, # NOSONAR justifies), nouveau db.json_for_script() (echappe
  "</script>" dans le JSON embarque en <script>, 25 sites).
- Architecture : imports circulaires/F811 nettoyes, contrats
  import-linter respectes, code mort retire (vulture).
- Accessibilite : 69 champs de formulaire sans label correctement
  associe corriges (for/id ou aria-label) sur 11 templates.
- ESLint/Stylelint : lot mecanique JS/CSS, regles ajustees puis
  appliquees (aucune desactivee sans verification individuelle).
- Tests : isolation du compte admin partage (nettoyage ponctuel +
  fixture de teardown automatique en filet de securite), suite complete
  verte (591 tests Python, 241 tests JS).
- SonarQube Community Build self-heberge (Docker + PostgreSQL) : rapport
  complet analyse point par point, faux positifs documentes.
- .gitattributes ajoute (LF force) : core.autocrlf=true sur cette machine
  faisait echouer ESLint (linebreak-style) via un bug connu de git
  (checkout "en place" qui ignore l'eol force sur un fichier deja
  present sur disque - contourne en supprimant puis recreant chaque
  fichier suivi).

djLint (H021, styles inline) volontairement saute pour ce commit -
backlog assume, deja documente, traite dans un lot separe.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

tests/test_scene_object_add_asset.py

@@ -1,20 +1,29 @@
 """Poser un objet de scène depuis "Mes assets" (voir plan Phase 1, §2) —
 routes/scenes/scene_object_add.py::asset_id, isolation stricte par
 propriétaire comme le reste de "Mes assets" (tests/test_user_assets.py)."""
-import re
+
+from collections.abc import Callable
+from typing import Any
+
+from flask.testing import FlaskClient
 
 import auth
 import screens
+from tests.conftest import not_none
 
 
-def _create_jeu2d_game(client, tmp_game_slug_cleanup, name="pytest_scene_object_asset"):
+def _create_jeu2d_game(
+    client: FlaskClient, tmp_game_slug_cleanup: Callable[[str], str], name: str = "pytest_scene_object_asset"
+) -> Any:
     resp = client.post("/games/new", data={"name": name}, follow_redirects=False)
     slug = tmp_game_slug_cleanup(resp.headers["Location"].rstrip("/").split("/")[-1])
     screen_id = screens.create_screen(slug, "Scène 1", kind="jeu_2d")
     return slug, screen_id
 
 
-def test_scene_object_add_with_asset_id_poses_the_owners_image(client, tmp_game_slug_cleanup):
+def test_scene_object_add_with_asset_id_poses_the_owners_image(
+    client: FlaskClient, tmp_game_slug_cleanup: Callable[[str], str]
+) -> None:
     slug, screen_id = _create_jeu2d_game(client, tmp_game_slug_cleanup)
     with client.session_transaction() as sess:
         user_id = sess["user_id"]
@@ -27,11 +36,14 @@ def test_scene_object_add_with_asset_id_poses_the_owners_image(client, tmp_game_
     )
     assert resp.status_code == 200
     body = resp.get_json()
-    obj = screens.get_scene_object(slug, body["id"])
+    obj = not_none(screens.get_scene_object(slug, body["id"]))
     assert obj["attributes"]["src"] == f"/assets/{user_id}/abc123.png"
+    auth.delete_user_asset(asset_id, user_id)
 
 
-def test_scene_object_add_with_asset_id_403s_for_another_accounts_asset(client, user_client, tmp_game_slug_cleanup):
+def test_scene_object_add_with_asset_id_403s_for_another_accounts_asset(
+    client: FlaskClient, user_client: FlaskClient, tmp_game_slug_cleanup: Callable[[str], str]
+) -> None:
     slug, screen_id = _create_jeu2d_game(client, tmp_game_slug_cleanup)
     with user_client.session_transaction() as sess:
         other_user_id = sess["user_id"]