Style settings sections with colored border titles

Each section gets a distinct color: General (purple), Email (green),
SSH (yellow), Web Dashboard (blue) — with background-colored title
labels matching the Textual markup playground style.

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

tui/gniza.tcss

@@ -88,11 +88,34 @@ Select {
 
 .settings-section {
     height: auto;
-    border: round $accent;
     padding: 1 2;
     margin: 0 0 1 0;
 }
 
+#section-general {
+    border: round #6e54c9;
+    border-title-color: #ffffff;
+    border-title-background: #6e54c9;
+}
+
+#section-email {
+    border: round #00cc00;
+    border-title-color: #ffffff;
+    border-title-background: #00cc00;
+}
+
+#section-ssh {
+    border: round #e5c07b;
+    border-title-color: #1e1e2e;
+    border-title-background: #e5c07b;
+}
+
+#section-web {
+    border: round #61afef;
+    border-title-color: #ffffff;
+    border-title-background: #61afef;
+}
+
 .settings-section Static {
     margin: 0;
 }