fix(redesign): a11y, mobile, perf polish for production push

Comprehensive pre-production sweep across the Aurora redesign — drives
svelte-check to 0 errors / 0 warnings (was 61) without changing visual
intent. Highlights:

- Mobile: hero title shrinks at 480px, signal-list stacks timestamp
  under sentence below 640px, sidebar icon buttons bumped to 40x40
- Light theme: muted-foreground darkened to #3a3560 to clear WCAG AA
  on glass surfaces and the modal close button
- Perf: topbar backdrop-filter 28→14px, mobile-more sheet 28→12px to
  cut concurrent blur layers on mid-tier mobile
- a11y: prefers-reduced-motion mute for aurora drift / pulses /
  shimmer / stagger; aria-label on every icon-only button;
  aria-describedby on Hint; combobox/listbox/aria-activedescendant on
  SearchPalette; modal dialog tabindex; 47 label-without-control
  warnings across 14 form pages cleaned up via for=/id= or label→div
- Dashboard derived state split into topology- vs status-bound layers
  so polling no longer re-runs the full provider/wires computation
- Mobile bottom nav derived from baseNavEntries by key lookup so
  adding a top-level nav entry keeps the two trees in sync
- Bug: template-configs page now respects the global provider filter
  for both the count meter and the type pill (was reading the
  unfiltered cache)
- Misc: portal EventChart tooltip and switch its swatches to Aurora
  tokens; CollapsibleSlot warning state uses warning-fg/-bg tokens
  instead of #d97706; Hint z-index 99999→9999; element refs across
  Modal/EntitySelect/MultiEntitySelect/SearchPalette/IconGridSelect/
  Hint/targets converted to \$state for reactivity; 4 dead
  .topbar-cta selectors removed

frontend/src/lib/components/CollapsibleSlot.svelte

@@ -21,7 +21,7 @@
 	const STATUS_MAP: Record<string, { icon: string; color: string; bg: string }> = {
 		empty: { icon: 'mdiCircleOutline', color: 'var(--color-muted-foreground)', bg: 'transparent' },
 		valid: { icon: 'mdiCheckCircle', color: 'var(--color-success-fg)', bg: 'var(--color-success-bg)' },
-		warning: { icon: 'mdiAlert', color: '#d97706', bg: 'rgba(217, 119, 6, 0.1)' },
+		warning: { icon: 'mdiAlert', color: 'var(--color-warning-fg)', bg: 'var(--color-warning-bg)' },
 		error: { icon: 'mdiAlertCircle', color: 'var(--color-error-fg)', bg: 'var(--color-error-bg)' },
 	};
 	const statusConfig = $derived(STATUS_MAP[status]);