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

src/components/Modal.module.css

@@ -0,0 +1,63 @@
+.modal {
+    display: none;
+    position: fixed;
+    top: 0;
+    left: 0;
+    width: 100%;
+    height: 100%;
+    background-color: rgba(0, 0, 0, 0.7);
+    z-index: 1000;
+}
+.modal.show {
+    display: flex;
+    justify-content: center;
+    align-items: center;
+}
+.modal-content {
+    background-color: #2a2a2a;
+    padding: 20px;
+    border-radius: 10px;
+    width: 90%;
+    max-width: 500px;
+    position: relative;
+}
+.modal-header {
+    display: flex;
+    justify-content: space-between;
+    align-items: center;
+    margin-bottom: 20px;
+}
+.close-button {
+    font-size: 24px;
+    cursor: pointer;
+    color: #888;
+}
+.close-button:hover {
+    color: white;
+}
+.modal-body {
+    margin-bottom: 20px;
+}
+.modal-footer {
+    display: flex;
+    justify-content: flex-end;
+    gap: 10px;
+}
+.modal-button {
+    padding: 8px 16px;
+    border: none;
+    border-radius: 5px;
+    cursor: pointer;
+    font-size: 16px;
+}
+.modal-button.cancel {
+    background-color: #444;
+    color: white;
+}
+.modal-button.confirm {
+    background-color: #e74c3c;
+    color: white;
+}
+.modal-button:hover {
+    opacity: 0.9;
+}