Fix/pylint cleanup (#8)

* Fix pylint warnings across all 24 Python files in web_server

- Add module, class, and function docstrings (C0114, C0115, C0116)
- Fix import ordering: stdlib before third-party before local (C0411)
- Replace wildcard imports with explicit named imports (W0401)
- Remove trailing whitespace and add missing final newlines (C0303, C0304)
- Replace dict() with dict literals (R1735)
- Remove unused imports and variables (W0611, W0612)
- Narrow broad Exception catches to specific exceptions (W0718)
- Replace f-string logging with lazy % formatting (W1203)
- Fix variable naming: UPPER_CASE for constants, snake_case for locals (C0103)
- Add pylint disable comments for necessary global statements (W0603)
- Fix no-else-return, simplifiable-if-expression, singleton-comparison
- Fix bad indentation in stripe.py (W0311)
- Add encoding="utf-8" to open() calls (W1514)
- Add check=True to subprocess.run() calls (W1510)
- Register Celery task modules via conf.include

* Update `package-lock.json` add peer dependencies

web_server/celery_tasks/celery_app.py

@@ -1,4 +1,6 @@
+"""Celery app initialization with Flask."""
+
 from blueprints import create_app
 
 flask_app = create_app()
-celery_app = flask_app.extensions["celery"]
+celery_app = flask_app.extensions["celery"]