feat(v0.3): QR connect (M5) + PWA installable (M4)

- M5: 📱 toolbar button → modal with a client-side QR of location.origin
  (shareable when opened via the LAN IP) + localhost tip
- M4: manifest.webmanifest + icon.svg + sw.js (network-first, never intercepts
  /term or /hook) + registration in main.ts; apple-touch + theme-color meta
- Browser-verified: QR canvas renders, SW 'controlled', manifest linked,
  no console errors. 199 tests green, build ok.

public/icon.svg

@@ -0,0 +1,7 @@
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 512 512" width="512" height="512">
+  <rect width="512" height="512" rx="96" fill="#1a1a1a"/>
+  <g fill="none" stroke="#3fb950" stroke-width="34" stroke-linecap="round" stroke-linejoin="round">
+    <polyline points="150,196 226,256 150,316"/>
+    <line x1="268" y1="320" x2="372" y2="320"/>
+  </g>
+</svg>