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/style.css

@@ -107,6 +107,52 @@ html, body {
   background: #555;
 }
 
+/* QR connect modal (M5) */
+#qrmodal {
+  position: fixed;
+  inset: 0;
+  z-index: 1200;
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  background: rgba(0, 0, 0, 0.6);
+}
+.qr-card {
+  background: #fff;
+  color: #111;
+  border-radius: 12px;
+  padding: 20px;
+  text-align: center;
+  max-width: 90vw;
+  box-shadow: 0 8px 32px rgba(0, 0, 0, 0.5);
+}
+.qr-title {
+  font-weight: 600;
+  margin-bottom: 12px;
+}
+.qr-url {
+  margin-top: 10px;
+  font-size: 13px;
+  color: #333;
+  word-break: break-all;
+}
+.qr-note {
+  margin-top: 8px;
+  font-size: 12px;
+  color: #666;
+  max-width: 240px;
+}
+.qr-close {
+  margin-top: 14px;
+  padding: 6px 18px;
+  border: none;
+  border-radius: 6px;
+  background: #1a1a1a;
+  color: #fff;
+  cursor: pointer;
+  font: inherit;
+}
+
 .tab {
   display: flex;
   align-items: center;