feat(ui): introduce PferdReiterEingabe, NennungenTabelle, and NennungsMaske components

- Added `PferdReiterEingabe` for horse and rider selection with search functionality and keyboard navigation.
- Implemented `NennungenTabelle` to display filtered registrations based on selected horse or rider.
- Introduced `NennungsMaske` to combine search, table, and competition views for streamlined user interaction.
- Extended types with `Veranstalter` interface and mock data for better context and integration.
- Documented ÖTO-compliant tournament structure for frontend reference.

Signed-off-by: Stefan Mogeritsch <stefan.mo.co@gmail.com>

docs/06_Frontend/FIGMA/Vision_03/postcss.config.mjs

@@ -0,0 +1,15 @@
+/**
+ * PostCSS Configuration
+ *
+ * Tailwind CSS v4 (via @tailwindcss/vite) automatically sets up all required
+ * PostCSS plugins — you do NOT need to include `tailwindcss` or `autoprefixer` here.
+ *
+ * This file only exists for adding additional PostCSS plugins, if needed.
+ * For example:
+ *
+ * import postcssNested from 'postcss-nested'
+ * export default { plugins: [postcssNested()] }
+ *
+ * Otherwise, you can leave this file empty.
+ */
+export default {}