fix: override js-dos DaisyUI button properties (text-transform, height)

js-dos v8 uses DaisyUI which sets text-transform:uppercase, height:3rem
on .btn — these cascade through even after our specificity fix because
we didn't define those properties. Added explicit overrides.

frontend/src/app.css

@@ -98,7 +98,7 @@ h3 { font-size: 1.2rem; }
 /* ═══════════════════════════════════════════════════════════════
    BUTTONS
    ═══════════════════════════════════════════════════════════════ */
-/* Double-class selector to win specificity against injected CSS */
+/* Double-class selector to win specificity against js-dos DaisyUI .btn */
 .btn.btn {
   display: inline-flex;
   align-items: center;
@@ -112,6 +112,9 @@ h3 { font-size: 1.2rem; }
   font-size: 0.9rem;
   font-weight: 600;
   cursor: pointer;
+  text-transform: none;
+  height: auto;
+  line-height: normal;
   transition: all 0.15s ease;
 }
 .btn.btn:hover {