Add PWA infrastructure for iOS notification support

- Add manifest.json for proper PWA installation
- Add service worker (sw.js) for push notification handling
- Add ServiceWorkerProvider to register SW and manage notifications
- Generate PNG icons (192x192, 512x512) for iOS compatibility
- Update settings to show notification status and test button
- Use service worker showNotification for iOS Safari compatibility

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

scripts/generate-icons.mjs

@@ -0,0 +1,26 @@
+import sharp from "sharp";
+import { fileURLToPath } from "url";
+import { dirname, join } from "path";
+import { readFileSync, writeFileSync } from "fs";
+
+const __filename = fileURLToPath(import.meta.url);
+const __dirname = dirname(__filename);
+const publicDir = join(__dirname, "..", "public", "icons");
+
+const svgPath = join(publicDir, "icon.svg");
+const svgContent = readFileSync(svgPath, "utf-8");
+
+async function generateIcons() {
+  const sizes = [192, 512];
+
+  for (const size of sizes) {
+    const outputPath = join(publicDir, `icon-${size}.png`);
+    await sharp(Buffer.from(svgContent))
+      .resize(size, size)
+      .png()
+      .toFile(outputPath);
+    console.log(`Generated ${outputPath}`);
+  }
+}
+
+generateIcons().catch(console.error);