feat(ui): add PWA configuration with service worker and enhanced manifest

Adds service worker with network-first navigation (SPA fallback) and
cache-first static assets. Enhances web manifest with start_url, scope,
id, description, orientation, and maskable icon entry.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

ui/public/site.webmanifest

@@ -1,6 +1,14 @@
 {
+  "id": "/",
   "name": "Paperclip",
   "short_name": "Paperclip",
+  "description": "AI-powered project management and agent coordination platform",
+  "start_url": "/",
+  "scope": "/",
+  "display": "standalone",
+  "orientation": "any",
+  "theme_color": "#18181b",
+  "background_color": "#18181b",
   "icons": [
     {
       "src": "/android-chrome-192x192.png",
@@ -11,9 +19,12 @@
       "src": "/android-chrome-512x512.png",
       "sizes": "512x512",
       "type": "image/png"
+    },
+    {
+      "src": "/android-chrome-512x512.png",
+      "sizes": "512x512",
+      "type": "image/png",
+      "purpose": "maskable"
     }
-  ],
-  "theme_color": "#18181b",
-  "background_color": "#18181b",
-  "display": "standalone"
+  ]
 }

ui/public/sw.js

@@ -0,0 +1,60 @@
+const CACHE_NAME = "paperclip-v1";
+const STATIC_ASSETS = ["/", "/favicon.ico", "/favicon.svg"];
+
+self.addEventListener("install", (event) => {
+  event.waitUntil(
+    caches.open(CACHE_NAME).then((cache) => cache.addAll(STATIC_ASSETS))
+  );
+  self.skipWaiting();
+});
+
+self.addEventListener("activate", (event) => {
+  event.waitUntil(
+    caches.keys().then((keys) =>
+      Promise.all(
+        keys
+          .filter((key) => key !== CACHE_NAME)
+          .map((key) => caches.delete(key))
+      )
+    )
+  );
+  self.clients.claim();
+});
+
+self.addEventListener("fetch", (event) => {
+  const { request } = event;
+  const url = new URL(request.url);
+
+  // Skip non-GET requests and API calls
+  if (request.method !== "GET" || url.pathname.startsWith("/api")) {
+    return;
+  }
+
+  // Network-first for navigation requests (SPA)
+  if (request.mode === "navigate") {
+    event.respondWith(
+      fetch(request)
+        .then((response) => {
+          const clone = response.clone();
+          caches.open(CACHE_NAME).then((cache) => cache.put(request, clone));
+          return response;
+        })
+        .catch(() => caches.match("/"))
+    );
+    return;
+  }
+
+  // Cache-first for static assets
+  event.respondWith(
+    caches.match(request).then((cached) => {
+      if (cached) return cached;
+      return fetch(request).then((response) => {
+        if (response.ok && url.origin === self.location.origin) {
+          const clone = response.clone();
+          caches.open(CACHE_NAME).then((cache) => cache.put(request, clone));
+        }
+        return response;
+      });
+    })
+  );
+});

ui/src/main.tsx

@@ -15,6 +15,12 @@ import { TooltipProvider } from "@/components/ui/tooltip";
 import "@mdxeditor/editor/style.css";
 import "./index.css";
 
+if ("serviceWorker" in navigator) {
+  window.addEventListener("load", () => {
+    navigator.serviceWorker.register("/sw.js");
+  });
+}
+
 const queryClient = new QueryClient({
   defaultOptions: {
     queries: {