feat: add PWA install icon and uppercase branding

src/client/public/favicon.svg

@@ -1,5 +1,5 @@
 <svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 1024 1024" role="img" aria-labelledby="title desc">
-  <title id="title">piweb mark</title>
+  <title id="title">PI WEB mark</title>
   <desc id="desc">A horizontal brand bar.</desc>
   <style>
     .bar { fill: #00f0d8; }

src/client/public/manifest.webmanifest

@@ -0,0 +1,24 @@
+{
+  "name": "PI WEB",
+  "short_name": "PI WEB",
+  "description": "Remote web UI and browser control plane for persistent Pi Coding Agent sessions.",
+  "start_url": "/",
+  "scope": "/",
+  "display": "standalone",
+  "background_color": "#0d1117",
+  "theme_color": "#0d1117",
+  "icons": [
+    {
+      "src": "/pwa-icon-192.png",
+      "sizes": "192x192",
+      "type": "image/png",
+      "purpose": "any maskable"
+    },
+    {
+      "src": "/pwa-icon-512.png",
+      "sizes": "512x512",
+      "type": "image/png",
+      "purpose": "any maskable"
+    }
+  ]
+}