fix(styles): resolve design system audit violations and touch scrolling

- Replace hardcoded px values with design tokens (--space-0h, --space-px,
  --space-1, --target-sm/md/lg) across layout, calendar, dashboard CSS
- Fix rgba(255,255,255,0.35) spinner border to use var(--color-glass-hover)
- Fix modal close icon from off-grid 18px to 16px
- Fix touch scrolling on mobile: add min-height: 0 and
  -webkit-overflow-scrolling: touch to .app-content

public/styles/calendar.css

@@ -69,10 +69,10 @@
 
 .cal-toolbar__views {
   display: flex;
-  gap: 2px;
+  gap: var(--space-0h);
   background-color: var(--color-surface-2);
   border-radius: var(--radius-sm);
-  padding: 2px;
+  padding: var(--space-0h);
 }
 
 .cal-toolbar__view-btn {
@@ -197,7 +197,7 @@
 .month-day__more {
   font-size: var(--text-xs);
   color: var(--color-text-secondary);
-  padding: 1px 4px;
+  padding: var(--space-px) var(--space-1);
   cursor: pointer;
 }