feat(pwa): enable SvelteKit service worker registration

Story 4: Enable SvelteKit Service Worker Registration
- Enable serviceWorker.register: true in svelte.config.js
- SvelteKit now handles service worker registration automatically
- Service worker builds successfully as service-worker.mjs
- Build and preview work without conflicts
- Ready for comprehensive testing

Migration to native SvelteKit PWA implementation complete

Refs: docs/plans/MigrateToNativeSvelteKitPWA.md

secrets/auth.json

@@ -5,7 +5,7 @@
       "value": "SDRORLyWEsWWty2ZoVGdER",
       "domain": ".instagram.com",
       "path": "/",
-      "expires": 1800937709.288068,
+      "expires": 1800937806.887488,
       "httpOnly": false,
       "secure": true,
       "sameSite": "Lax"
@@ -45,7 +45,7 @@
       "value": "59661903731",
       "domain": ".instagram.com",
       "path": "/",
-      "expires": 1774153709.288173,
+      "expires": 1774153806.887596,
       "httpOnly": false,
       "secure": true,
       "sameSite": "None"
@@ -55,7 +55,7 @@
       "value": "1280x720",
       "domain": ".instagram.com",
       "path": "/",
-      "expires": 1766982509,
+      "expires": 1766982607,
       "httpOnly": false,
       "secure": true,
       "sameSite": "Lax"
@@ -72,7 +72,7 @@
     },
     {
       "name": "rur",
-      "value": "\"CLN\\05459661903731\\0541797913709:01fe9901d778068c1e12d177d918913a9e0ac541b803518c6f5cbdc54e966f512cdfd807\"",
+      "value": "\"CLN\\05459661903731\\0541797913806:01feeb043986a2466aaaf1ebeba09fae2ba7a82be022a7c9d571d4776f15f3e124c3a5a6\"",
       "domain": ".instagram.com",
       "path": "/",
       "expires": -1,
@@ -87,7 +87,7 @@
       "localStorage": [
         {
           "name": "chatd-deviceid",
-          "value": "e55831d9-52f6-4b3b-a96a-cc3125af6b01"
+          "value": "fade0988-9ed7-4eef-8138-bd47b59f9bee"
         },
         {
           "name": "hb_timestamp",
@@ -95,11 +95,7 @@
         },
         {
           "name": "IGSession",
-          "value": "kc8y0b:1766379509344"
-        },
-        {
-          "name": "mutex_polaris_banzai",
-          "value": "yd2eoe:1766377710344"
+          "value": "kc8y0b:1766379608038"
         },
         {
           "name": "pixel_fire_ts",
@@ -111,16 +107,12 @@
         },
         {
           "name": "Session",
-          "value": "nseh2f:1766377744344"
+          "value": "of2mur:1766377843038"
         },
         {
           "name": "has_interop_upgraded",
           "value": "{\"lastCheckedAt\":1766366944051,\"status\":false}"
         },
-        {
-          "name": "mutex_banzai",
-          "value": "yd2eoe:1766377710344"
-        },
         {
           "name": "banzai:last_storage_flush",
           "value": "1766366944520.7"