feat: modularize scanner, enhance carousel preloading, and improve PWA updates

Summary of changes:
- Extracted archive scanning logic into a modular 'useArchiveScanner' hook for better maintainability and performance.
- Refined PostModal carousel with intelligent media preloading and smoother, jitter-free transitions.
- Optimized image rendering with 'decoding=async' and removed 'black flashes' between slide changes.
- Updated PWA configuration to 'autoUpdate' with hourly periodic checks for fresh content.
- Fixed several bugs including stories sorting, permalink parameter cleanup, and profile metadata cache restoration.
- Comprehensive updates to documentation (README.md and GEMINI.md) reflecting the new architecture.

vite.config.ts

@@ -11,7 +11,7 @@ export default defineConfig(({mode}) => {
       react(), 
       tailwindcss(),
       VitePWA({
-        registerType: 'prompt',
+        registerType: 'autoUpdate',
         manifest: {
           name: 'InstaArchive',
           short_name: 'InstaArchive',