Add PWA install badge for desktop and tablet (manifest, SW, Add to Home Screen).

Co-authored-by: Cursor <cursoragent@cursor.com>

frontend/src/styles/app.css

@@ -89,6 +89,65 @@ input {
   text-overflow: ellipsis;
 }
 
+.install-wrap {
+  position: relative;
+  flex-shrink: 0;
+}
+
+.install-btn {
+  font-size: 12px;
+  padding: 4px 10px;
+  border: 1px solid var(--line);
+  color: var(--accent);
+}
+
+.install-badge {
+  display: inline-flex;
+  align-items: center;
+  font-size: 11px;
+  font-weight: 600;
+  letter-spacing: 0.04em;
+  padding: 3px 8px;
+  border-radius: 4px;
+  white-space: nowrap;
+}
+
+.install-badge.installed {
+  color: #0b0e11;
+  background: var(--accent);
+}
+
+.install-tip {
+  position: absolute;
+  top: calc(100% + 8px);
+  left: 0;
+  z-index: 30;
+  width: min(320px, calc(100vw - 24px));
+  padding: 12px;
+  border: 1px solid var(--line);
+  border-radius: 8px;
+  background: var(--bg-elev);
+  box-shadow: 0 8px 24px rgba(0, 0, 0, 0.45);
+}
+
+.install-tip p {
+  margin: 0 0 8px;
+  font-size: 12px;
+  line-height: 1.5;
+  color: var(--text);
+}
+
+.install-tip p.muted,
+.install-tip .muted {
+  color: var(--muted);
+}
+
+@media (max-width: 900px) {
+  .topnav-side.left .brand {
+    max-width: 9em;
+  }
+}
+
 .topnav a {
   color: var(--muted);
   text-decoration: none;
@@ -340,10 +399,18 @@ input {
 }
 
 .login-box h1 {
-  margin: 0 0 6px;
+  margin: 0;
   font-size: 22px;
 }
 
+.login-title-row {
+  display: flex;
+  align-items: flex-start;
+  justify-content: space-between;
+  gap: 10px;
+  margin-bottom: 6px;
+}
+
 .login-box p {
   margin: 0 0 20px;
   color: var(--muted);