feat: switch from PaperMod to Congo theme

- Warm avocado color scheme, light mode default — friendly for families
- Congo language configs in config/_default/languages.{en,de}.toml
- Renamed extend partials to Congo convention (hyphens)
- Override warnings.html for Hugo 0.159 compatibility (.Author removed)
- All shortcodes and custom partials preserved

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

config/_default/languages.de.toml

@@ -0,0 +1,26 @@
+languageCode = "de"
+languageName = "Deutsch"
+languageDirection = "ltr"
+weight = 2
+
+title = "Internet für Kinder"
+
+[params]
+  description = "Experteneinblicke zu Kinderschutzgesetzen, Online-Sicherheit und digitalem Familienschutz weltweit."
+
+[params.author]
+  name = "Agiliton"
+  headline = "Kinder online schützen"
+  bio = "Experteneinblicke zu Kinderschutzgesetzen, Online-Sicherheit und digitalem Familienschutz weltweit."
+
+[[menus.main]]
+  identifier = "about"
+  name = "Über uns"
+  url = "/about/"
+  weight = 2
+
+[[menus.main]]
+  identifier = "tags"
+  name = "Themen"
+  url = "/tags/"
+  weight = 3