Remove email notifications for exceptions, route to Sentry only

[Copilot]

Django's AdminEmailHandler was configured alongside Sentry, causing exceptions to be emailed to admins redundantly. Sentry already captures all exceptions via sentry_sdk with DjangoIntegration.

Changes

• blt/settings.py: Removed mail_admins handler (django.utils.log.AdminEmailHandler) from LOGGING and dropped it from the django logger's handler list

# Before
"handlers": {
    "console": { ... },
    "mail_admins": {"level": "ERROR", "class": "django.utils.log.AdminEmailHandler"},
},
"loggers": {
    "django": {
        "handlers": ["console", "mail_admins"],
        ...
    },

# After
"handlers": {
    "console": { ... },
},
"loggers": {
    "django": {
        "handlers": ["console"],
        ...
    },

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[Copilot]

Pull request overview

Removes Django’s admin exception email logging so that exceptions are reported via Sentry only, avoiding redundant notifications.

Changes:

• Removed the django.utils.log.AdminEmailHandler (mail_admins) handler from LOGGING.
• Updated the django logger to no longer reference mail_admins.

[Copilot]

With mail_admins removed from the django logger, production exception notifications will now rely entirely on Sentry. Since sentry_sdk.init(...) is conditional on SENTRY_DSN being set, environments without SENTRY_DSN configured will no longer emit any exception alerts. Consider enforcing SENTRY_DSN when DEBUG is False (fail fast) or adding an explicit fallback handler for error-level logs in non-debug environments.