fix(home): stop iOS Safari zooming on the interval-minutes input

iOS auto-zooms <input> elements when their font-size is below 16px. The
"every X minutes" number field was using --text-sm (13px), so tapping it
zoomed the page — unwanted on a PWA. Bumped to 16px to suppress the zoom.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

frontend/src/views/HomeView.vue

@@ -809,7 +809,9 @@ async function saveSettings() {
     border-radius: var(--radius-md);
     background: var(--color-surface);
     color: var(--color-text);
-    font-size: var(--text-sm);
+    // iOS Safari auto-zooms <input> when font-size < 16px. Use 16px+ to prevent
+    // the page from zooming when the user taps the number field.
+    font-size: 16px;
     font-family: inherit;
     text-align: center;