fix: bust service worker cache on each build with version+timestamp

The SW cache name was hardcoded to 'pinchchat-v1', meaning PWA users
would get stale cached assets forever. Now the cache name includes
the package version and build timestamp, so each build creates a new
cache and old ones are cleaned up on activation.

Also adds:
- Periodic SW update check (every 30 min)
- Auto-reload when new SW version is detected

public/sw.js

@@ -1,5 +1,5 @@
 // PinchChat Service Worker — cache static assets for offline/instant load
-const CACHE_NAME = 'pinchchat-v1';
+const CACHE_NAME = 'pinchchat-__SW_VERSION__';
 
 // Cache static assets on install
 self.addEventListener('install', (event) => {

src/main.tsx

@@ -8,7 +8,24 @@ import './index.css'
 // Register service worker for PWA support (offline caching, installability)
 if ('serviceWorker' in navigator) {
   window.addEventListener('load', () => {
-    navigator.serviceWorker.register('/sw.js').catch(() => {
+    navigator.serviceWorker.register('/sw.js').then((reg) => {
+      // Check for updates periodically (every 30 min)
+      setInterval(() => reg.update().catch(() => {}), 30 * 60 * 1000);
+
+      // When a new SW is installed and waiting, reload to activate it
+      reg.addEventListener('updatefound', () => {
+        const newWorker = reg.installing;
+        if (!newWorker) return;
+        newWorker.addEventListener('statechange', () => {
+          if (newWorker.state === 'installed' && navigator.serviceWorker.controller) {
+            // New version available — reload on next navigation
+            // The new SW called skipWaiting(), so it activates immediately
+            // Reload to pick up cached assets from the new cache version
+            window.location.reload();
+          }
+        });
+      });
+    }).catch(() => {
       // SW registration failed — app works fine without it
     });
   });

vite.config.ts

@@ -1,13 +1,33 @@
-import { defineConfig } from 'vite'
+import { defineConfig, type Plugin } from 'vite'
 import react from '@vitejs/plugin-react'
 import tailwindcss from '@tailwindcss/vite'
+import { readFileSync, writeFileSync, existsSync } from 'node:fs'
+import { resolve, dirname } from 'node:path'
+import { fileURLToPath } from 'node:url'
 import pkg from './package.json' with { type: 'json' }
 
+const __dirname = dirname(fileURLToPath(import.meta.url))
+
+/** Replace __SW_VERSION__ in sw.js with version+timestamp at build time */
+function swVersionPlugin(): Plugin {
+  const version = `${pkg.version}-${Date.now()}`
+  return {
+    name: 'sw-version',
+    closeBundle() {
+      const swPath = resolve(__dirname, 'dist', 'sw.js')
+      if (existsSync(swPath)) {
+        const content = readFileSync(swPath, 'utf-8')
+        writeFileSync(swPath, content.replace(/__SW_VERSION__/g, version))
+      }
+    },
+  }
+}
+
 export default defineConfig({
   define: {
     __APP_VERSION__: JSON.stringify(pkg.version),
   },
-  plugins: [react(), tailwindcss()],
+  plugins: [react(), tailwindcss(), swVersionPlugin()],
   build: {
     rollupOptions: {
       output: {