Fix settings modal overflowing viewport on smaller screens

Constrain modal height to viewport and make tab content scrollable
so the modal no longer falls off the bottom of the screen.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

static/css/settings.css

@@ -26,6 +26,9 @@
     border-radius: 8px;
     max-width: 600px;
     width: 100%;
+    max-height: calc(100vh - 80px);
+    display: flex;
+    flex-direction: column;
     position: relative;
     box-shadow: 0 20px 60px rgba(0, 0, 0, 0.5);
 }
@@ -115,6 +118,9 @@
 
 .settings-section.active {
     display: block;
+    overflow-y: auto;
+    flex: 1;
+    min-height: 0;
 }
 
 .settings-group {