Add PWA assets, update index.astro, set .gitea

- Added PWA-related files: LICENSE, favicon.ico, icon-192.png, icon-512.png, manifest.json, service-worker.js in public/
- Deleted legacy favicon.svg
- Major update to src/pages/index.astro: implements full responsive UI, PWA manifest, service worker registration, and touch/mobile optimizations
- Added/updated .gitea to track current Gitea issue for workflow compliance

Purpose: Implements PWA support and refactors the main page for the Astro app, aligning with the migration and refactor described in issue #1.

Refs #1

public/service-worker.js

@@ -0,0 +1,31 @@
+const CACHE_NAME = 'bscscore-v1';
+const URLS_TO_CACHE = [
+  '/',
+  '/index.html',
+  '/manifest.json',
+  '/favicon.ico',
+  '/icon-192.png',
+  '/icon-512.png'
+];
+
+self.addEventListener('install', event => {
+  event.waitUntil(
+    caches.open(CACHE_NAME).then(cache => cache.addAll(URLS_TO_CACHE))
+  );
+});
+
+self.addEventListener('activate', event => {
+  event.waitUntil(
+    caches.keys().then(keys =>
+      Promise.all(keys.filter(key => key !== CACHE_NAME).map(key => caches.delete(key)))
+    )
+  );
+});
+
+self.addEventListener('fetch', event => {
+  event.respondWith(
+    caches.match(event.request).then(response =>
+      response || fetch(event.request).catch(() => caches.match('/index.html'))
+    )
+  );
+});