refactor(webapp): remove emoji web app logo option

Drop the emoji-logo feature (and its font picker) from the Web App. Only
an uploaded/linked image logo and favicon remain; when no logo is set,
the default project logo is shown. Existing emoji-logo overrides are
ignored — the keys are gone from the manifest, so the override service
skips them and the app falls back to the default logo.

- Remove WEBAPP_LOGO_USE_EMOJI / WEBAPP_LOGO_EMOJI / WEBAPP_LOGO_EMOJI_FONT
  settings, validators, manifest entries and override/runtime plumbing.
- Strip the animated-emoji fetch/cache subsystem, the /webapp-emoji route
  and emoji branches from logo/favicon resolution; leftover emoji cache
  files are now purged on appearance save.
- Simplify BrandMark to an image-only component and drop the emoji UI
  from the admin Appearance section.
- Regenerate the demo settings manifest and clean docs, locales, nginx
  and demo data of emoji-logo references.

tests/test_user_email_notifications.py

@@ -38,7 +38,6 @@ def _settings(**overrides):
         "WEBAPP_PRIMARY_COLOR": "#00fe7a",
         "WEBAPP_TITLE": "Mini Shop",
         "WEBAPP_LOGO_URL": "",
-        "WEBAPP_LOGO_USE_EMOJI": False,
     }
     values.update(overrides)
     return SimpleNamespace(**values)