feat: add feature toggle system for disabling modules and UI

[JacobCoffee]

Summary

• Add FeaturesConfig dataclass for module/UI toggles via DJANGO_PROGRAM["features"] settings
• Add DB-backed FeatureFlags model (per-conference, OneToOneField) for live runtime toggling via Django admin
• Priority: DB overrides > settings defaults. None in DB = use settings default, explicit True/False = override
• Add features.py with is_feature_enabled(feature, conference=None), require_feature(), and FeatureRequiredMixin
• Add context processor for template-level feature checks (registered in example app)
• Master switch all_ui_enabled overrides both public and manage UI (from settings or DB)
• All features enabled by default - opt-in to disable
• 63 tests covering all toggle logic, DB overrides, backward compatibility

How to test in the UI

1. Start the dev server:

   uv run python examples/manage.py migrate
   uv run python examples/manage.py runserver

2. Create a superuser if needed:

   uv run python examples/manage.py createsuperuser

3. Go to Django Admin at /admin/

4. Navigate to Conference > Feature flags and click "Add"

5. Select a conference and toggle features:

   • Leave fields blank (None) to use settings defaults
   • Set to True or False to override for that specific conference
   • Changes take effect immediately — no restart needed

6. Test the master switch:

   • Set all_ui_enabled to False in the admin
   • Both public and manage UI should return 404 for that conference

7. Test individual toggles:

   • Set registration_enabled to False
   • Registration-related views should 404 (when FeatureRequiredMixin is applied in follow-up)

8. Settings.py still works as global defaults:

   DJANGO_PROGRAM = {
       "features": {
           "registration_enabled": False,  # global default
       },
   }

   A conference can then re-enable it via the admin by setting its DB flag to True.

Test plan

• All features enabled by default with no config or DB rows
• DB FeatureFlags with explicit False disables feature for that conference
• DB FeatureFlags with None falls back to settings default
• all_ui_enabled=False in DB disables both public_ui and manage_ui
• Settings-level defaults work when no DB row exists
• Context processor exposes resolved flags to templates
• Django admin UI shows feature flags with clean fieldset layout
• Changes in admin take effect without restart

🤖 Generated with Claude Code

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