feat(pwa): add offline support, network-first service worker, web manifest & e-business card mode

public/manifest.webmanifest

@@ -0,0 +1,25 @@
+{
+  "name": "Cris Charles Garcia | Full-Stack Developer & E-Business Card",
+  "short_name": "Cris Charles",
+  "description": "Digital portfolio and e-business card of Cris Charles Garcia. Full-stack developer and Cisco certified specialist.",
+  "start_url": "/",
+  "display": "standalone",
+  "background_color": "#090a0f",
+  "theme_color": "#090a0f",
+  "orientation": "any",
+  "categories": ["portfolio", "business", "utilities"],
+  "icons": [
+    {
+      "src": "/logo.png",
+      "sizes": "192x192",
+      "type": "image/png",
+      "purpose": "any"
+    },
+    {
+      "src": "/logo.png",
+      "sizes": "512x512",
+      "type": "image/png",
+      "purpose": "any maskable"
+    }
+  ]
+}

public/sw.js

@@ -0,0 +1,99 @@
+const CACHE_NAME = 'portfolio-cache-v1';
+
+// Core assets to precache immediately on install
+const PRECACHE_ASSETS = [
+  '/',
+  '/manifest.webmanifest',
+  '/logo.png',
+  '/favicon.ico',
+  '/CV-Cris-Charles-Garcia.pdf'
+];
+
+// Install: precache shell
+self.addEventListener('install', (event) => {
+  event.waitUntil(
+    caches.open(CACHE_NAME).then((cache) => {
+      return cache.addAll(PRECACHE_ASSETS).catch((err) => {
+        console.warn('SW: Precache partial failure (non-critical):', err);
+      });
+    }).then(() => self.skipWaiting())
+  );
+});
+
+// Activate: clean up old cache versions
+self.addEventListener('activate', (event) => {
+  event.waitUntil(
+    caches.keys().then((cacheNames) => {
+      return Promise.all(
+        cacheNames
+          .filter((name) => name !== CACHE_NAME)
+          .map((name) => caches.delete(name))
+      );
+    }).then(() => self.clients.claim())
+  );
+});
+
+// Fetch: Network-First for HTML navigation, Stale-While-Revalidate for static assets
+self.addEventListener('fetch', (event) => {
+  const { request } = event;
+  const url = new URL(request.url);
+
+  // Skip non-GET requests and browser extensions
+  if (request.method !== 'GET' || !url.protocol.startsWith('http')) {
+    return;
+  }
+
+  // 1. Navigation requests (HTML pages): Network-First with Cache Fallback
+  if (request.mode === 'navigate') {
+    event.respondWith(
+      fetch(request)
+        .then((networkResponse) => {
+          if (networkResponse && networkResponse.status === 200) {
+            const responseClone = networkResponse.clone();
+            caches.open(CACHE_NAME).then((cache) => {
+              cache.put(request, responseClone);
+            });
+          }
+          return networkResponse;
+        })
+        .catch(async () => {
+          // Offline fallback
+          const cachedResponse = await caches.match(request);
+          if (cachedResponse) {
+            return cachedResponse;
+          }
+          // Fallback to home page root if specific subpage isn't cached
+          const rootCached = await caches.match('/');
+          if (rootCached) {
+            return rootCached;
+          }
+          return new Response(
+            '<!DOCTYPE html><html><head><meta charset="utf-8"><title>Offline - Cris Charles</title><meta name="viewport" content="width=device-width,initial-scale=1"></head><body style="font-family:sans-serif;background:#090a0f;color:#fff;display:flex;align-items:center;justify-content:center;height:100vh;margin:0;text-align:center;padding:20px;"><div><h1 style="font-size:1.8rem;margin-bottom:12px;">📶 Offline Mode</h1><p style="color:#888;max-width:400px;margin:0 auto 20px;">You are currently offline. Please reconnect to view new updates or visit previously cached pages.</p><a href="/" style="display:inline-block;padding:10px 20px;border-radius:12px;background:#3b82f6;color:#fff;text-decoration:none;font-weight:600;">Return to Home</a></div></body></html>',
+            { headers: { 'Content-Type': 'text/html' } }
+          );
+        })
+    );
+    return;
+  }
+
+  // 2. Static Assets (CSS, JS, WebP, SVG, Fonts, PNG): Stale-While-Revalidate
+  event.respondWith(
+    caches.match(request).then((cachedResponse) => {
+      const fetchPromise = fetch(request)
+        .then((networkResponse) => {
+          if (networkResponse && networkResponse.status === 200) {
+            const responseClone = networkResponse.clone();
+            caches.open(CACHE_NAME).then((cache) => {
+              cache.put(request, responseClone);
+            });
+          }
+          return networkResponse;
+        })
+        .catch(() => {
+          // Network failed, nothing extra to do if cached response is returned
+        });
+
+      return cachedResponse || fetchPromise;
+    })
+  );
+});