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.

deploy/docker/frontend/nginx.conf

@@ -84,7 +84,7 @@ server {
         proxy_set_header X-Forwarded-Proto $scheme;
     }
 
-    location ~ ^/(webapp-logo|webapp-uploaded-logo|webapp-favicon|webapp-emoji|webapp-theme-css|webapp-theme-assets)/ {
+    location ~ ^/(webapp-logo|webapp-uploaded-logo|webapp-favicon|webapp-theme-css|webapp-theme-assets)/ {
         proxy_pass http://backend:8081;
         proxy_http_version 1.1;
         proxy_set_header Host $host;