refactor: migrate UI to Preact components and remove legacy Astro/JS

- Replaced all .astro components with .jsx Preact components and added corresponding CSS modules.
- Updated index.astro to use the new App Preact component; removed legacy script and Astro imports.
- Deleted obsolete .astro component files and main JS logic (src/scripts/index.js, public/scripts/index.js).
- Updated astro.config.mjs for Preact integration.
- Updated package.json and package-lock.json to include @astrojs/preact and preact.
- Updated tsconfig.json for Preact JSX support.
- Refactored index.css to keep only global resets and utility styles.
- All changes relate to Gitea issue #1 (refactor to astro app).

Migrates the UI from Astro/vanilla JS to a modular Preact component architecture, removing all legacy code and aligning the project with modern best practices.
Refs #1

tsconfig.json

@@ -1,5 +1,14 @@
 {
   "extends": "astro/tsconfigs/strict",
-  "include": [".astro/types.d.ts", "**/*"],
-  "exclude": ["dist"]
-}
+  "include": [
+    ".astro/types.d.ts",
+    "**/*"
+  ],
+  "exclude": [
+    "dist"
+  ],
+  "compilerOptions": {
+    "jsx": "react-jsx",
+    "jsxImportSource": "preact"
+  }
+}