fix: change default theme to gitea-dark (built-in)

Custom themes not loading properly, reverting to built-in theme.
Custom themes still available in theme list for manual selection.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

dev/compose.yaml

@@ -41,8 +41,7 @@ services:
       GITEA__packages__ENABLED: true
       GITEA__actions__ENABLED: true
       GITEA__ui__THEMES: gitea-auto,gitea-light,gitea-dark,arc-green,edge-auto,edge-dark,edge-light,everforest-auto,everforest-dark,everforest-light,gruvbox-auto,gruvbox-dark,gruvbox-light,gruvbox-material-auto,gruvbox-material-dark,gruvbox-material-light,nord,palenight,soft-era,sonokai,sonokai-andromeda,sonokai-atlantis,sonokai-espresso,sonokai-maia,sonokai-shusia
-      GITEA__ui__DEFAULT_THEME: edge-dark
-      GITEA__ui__THEME_COLOR_META_TAG: "#333644"
+      GITEA__ui__DEFAULT_THEME: gitea-dark
       GITEA__ui__ENABLE_FEED: true
     networks:
       - compose_network