Add built-in theme support with various pre-defined themes

- Introduce multiple built-in themes (`default_dark`, `default_light`, `gruvbox`, `dracula`, `solarized`, `midnight-ocean`, `rose-pine`, `monokai`, `material-dark`, `material-light`).
- Implement theming system with customizable color schemes for all UI components in the TUI.
- Include documentation for themes in `themes/README.md`.
- Add fallback mechanisms for default themes in case of parsing errors.
- Support custom themes with overrides via configuration.

PKGBUILD

@@ -1,6 +1,6 @@
 # Maintainer: vikingowl <christian@nachtigall.dev>
 pkgname=owlen
-pkgver=0.1.8
+pkgver=0.1.9
 pkgrel=1
 pkgdesc="Terminal User Interface LLM client for Ollama with chat and code assistance features"
 arch=('x86_64')
@@ -40,5 +40,11 @@ package() {
 
     # Install documentation
     install -Dm644 README.md "$pkgdir/usr/share/doc/$pkgname/README.md"
+
+    # Install built-in themes for reference
+    install -Dm644 themes/README.md "$pkgdir/usr/share/$pkgname/themes/README.md"
+    for theme in themes/*.toml; do
+        install -Dm644 "$theme" "$pkgdir/usr/share/$pkgname/themes/$(basename $theme)"
+    done
 }