feat: Add Dracula and Everforest color themes, set Everforest as default

- Add DraculaTheme with official Dracula color palette
- Add EverforestTheme with natural Everforest dark color scheme
- Set Everforest as default theme (was 'default')
- Update README with theming documentation and THEME env var usage
- Build verified successfully

README.md

@@ -11,6 +11,36 @@ This project uses **beads** (`bd` CLI) for issue tracking and **Gitea** for exte
 - **Issue tracking**: Use `bd ready` to find available work
 - **External issues**: Gitea at https://gitea.calmcacil.dev
 
+## Theming
+
+The TUI supports multiple color themes. Set the `THEME` environment variable to switch themes:
+
+### Available Themes
+
+| Theme | Description | Default |
+|-------|-------------|---------|
+| `everforest` | Natural green/blue theme (default) | ✅ |
+| `dracula` | Popular dark purple theme | |
+| `default` | Standard blue-based theme | |
+| `dark` | Purple-based dark theme | |
+| `light` | Green-based light theme | |
+
+### Usage
+
+```bash
+# Use Everforest (default)
+sudo wg-admin-tui
+
+# Use Dracula theme
+THEME=dracula sudo wg-admin-tui
+
+# Use default theme
+THEME=default sudo wg-admin-tui
+
+# Use light theme
+THEME=light sudo wg-admin-tui
+```
+
 ## Configuration
 
 Configuration is managed through `/etc/wg-admin/config.conf`. Copy `config.example` to this location and customize for your environment.