Make topbar and tab bar sticky in web terminal

Adds position:sticky to the topbar and tab bar so they stay pinned
at the top when the virtual keyboard opens on tablets. Also uses
100dvh (dynamic viewport height) so the layout properly shrinks
when the keyboard appears on mobile browsers.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

app/src-tauri/src/web_terminal/terminal.html

@@ -30,6 +30,7 @@
     color: var(--text-primary);
     font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
     height: 100vh;
+    height: 100dvh; /* dynamic viewport height — shrinks when mobile keyboard opens */
     display: flex;
     flex-direction: column;
     overflow: hidden;
@@ -46,6 +47,9 @@
     border-bottom: 1px solid var(--border);
     flex-shrink: 0;
     min-height: 42px;
+    position: sticky;
+    top: 0;
+    z-index: 20;
   }
 
   .topbar-title {
@@ -101,6 +105,9 @@
     overflow-x: auto;
     -webkit-overflow-scrolling: touch;
     min-height: 32px;
+    position: sticky;
+    top: 42px; /* below .topbar min-height */
+    z-index: 20;
   }
 
   .tab {