Add boost-mailing-list-tracker app

[snowfox1003]

This app is for tracking Boost mailing list.

1. Required for new app

• Models – Define in models.py, add migrations, update Schema.md if the project uses it.
• Services – All writes to app models go through the service layer (services.py).
• Commands – Management command in management/commands/run_boost_mailing_list_tracker.py; use proper exit codes (0 / non-zero).
• Service API doc – Add docs/service_api/boost_mailing_list_tracker.md and a row in docs/service_api/README.md.
• Install – Add the app to INSTALLED_APPS in settings.
• Collectors – If it’s a collector, add its command to run_all_collectors in the right order.

2. Add only when they apply

• Workspace docs – Document in Workspace.md only if the app uses the shared workspace (file storage).
• Operations + docs – Add an operations doc only if the app introduces a shared external I/O layer (e.g. GitHub, Discord) used by other apps.

3. Good to have

• Admin – Register models in admin.py if they should be editable in Django admin.
• Restart/resume – Command skips already-processed work when re-run.
• Logging – Use project logging (e.g. logging.getLogger(name)).
• Tests – Add tests for new behavior.

[henry0816191]

#41