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_settings.py

@@ -127,9 +127,6 @@ class SettingsTests(unittest.TestCase):
             POSTGRES_PASSWORD="app_password",
             WEBAPP_PRIMARY_COLOR="#ff0000",
             WEBAPP_LOGO_URL="https://cdn.example.com/logo.png",
-            WEBAPP_LOGO_USE_EMOJI=True,
-            WEBAPP_LOGO_EMOJI="🔥",
-            WEBAPP_LOGO_EMOJI_FONT="twemoji",
             WEBAPP_FAVICON_USE_CUSTOM=True,
             WEBAPP_FAVICON_URL="https://cdn.example.com/favicon.png",
             WEBAPP_LOGO_FAVICON_URL="/webapp-favicon/abcdef1234567890/icon-180.png",
@@ -137,9 +134,6 @@ class SettingsTests(unittest.TestCase):
 
         self.assertEqual(settings.WEBAPP_PRIMARY_COLOR, "#00fe7a")
         self.assertIsNone(settings.WEBAPP_LOGO_URL)
-        self.assertFalse(settings.WEBAPP_LOGO_USE_EMOJI)
-        self.assertEqual(settings.WEBAPP_LOGO_EMOJI, "🫥")
-        self.assertEqual(settings.WEBAPP_LOGO_EMOJI_FONT, "system")
         self.assertFalse(settings.WEBAPP_FAVICON_USE_CUSTOM)
         self.assertIsNone(settings.WEBAPP_FAVICON_URL)
         self.assertIsNone(settings.WEBAPP_LOGO_FAVICON_URL)
@@ -202,7 +196,6 @@ class SettingsTests(unittest.TestCase):
             POSTGRES_PASSWORD="app_password",
         )
         settings.WEBAPP_LOGO_URL = "/webapp-uploaded-logo/logo-1111111111111111.png"
-        settings.WEBAPP_LOGO_USE_EMOJI = False
         settings.WEBAPP_LOGO_FAVICON_URL = "/webapp-favicon/aaaaaaaaaaaaaaaa/icon-180.png"
         settings.WEBAPP_FAVICON_USE_CUSTOM = True
         settings.WEBAPP_FAVICON_URL = "/webapp-favicon/bbbbbbbbbbbbbbbb/icon-180.png"