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/routes/notification-trackers/LinkedTargetsSection.svelte

@@ -129,13 +129,13 @@
 					<div class="px-2.5 pb-2.5" in:slide={{ duration: 150 }}>
 						<div class="grid grid-cols-2 gap-2">
 							<div>
-								<label class="block text-xs text-[var(--color-muted-foreground)] mb-1">{t('trackingConfig.title')}</label>
+								<div class="block text-xs text-[var(--color-muted-foreground)] mb-1">{t('trackingConfig.title')}</div>
 								<EntitySelect items={trackingConfigItems} value={tt.tracking_config_id}
 									placeholder={t('common.noneDefault')} size="sm" allowNone noneLabel={t('common.noneDefault')}
 									onselect={(v) => onupdateLink(tt, 'tracking_config_id', Number(v) || null)} />
 							</div>
 							<div>
-								<label class="block text-xs text-[var(--color-muted-foreground)] mb-1">{t('templateConfig.title')}</label>
+								<div class="block text-xs text-[var(--color-muted-foreground)] mb-1">{t('templateConfig.title')}</div>
 								<EntitySelect items={templateConfigItems} value={tt.template_config_id}
 									placeholder={t('common.noneDefault')} size="sm" allowNone noneLabel={t('common.noneDefault')}
 									onselect={(v) => onupdateLink(tt, 'template_config_id', Number(v) || null)} />