CMS 2.0 - Theme engine, logging, admin improvements

Major changes:
- New ThemeManager with Twig templating and SCSS compilation
- Dynamic themes system (themes/default, themes/demo)
- LogManager with SQLite storage and syslog forwarding
- RequestLogger with static helper methods
- Admin UI overhaul (Bootstrap 5, dark mode)
- Admin config page with logging and theme settings
- Admin logs page with filters and search
- Removed legacy Mustache templates
- Removed test plugin and theme
- Composer dependencies: Twig, scssphp, CommonMark, MaxMind GeoIP

.gitignore

@@ -20,6 +20,9 @@ admin/storage/cache/
 admin/storage/geoip/
 admin/storage/stats.json
 
+# Runtime-compiled theme assets
+public/themes/
+
 # Temporary files
 *.tmp
 *.temp