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/settings/backup/+page.svelte

@@ -343,7 +343,7 @@
 			<!-- Categories -->
 			<div class="mb-4">
 				<div class="flex items-center gap-2 mb-2">
-					<label class="text-xs font-medium">{t('backup.categories')}</label>
+					<span class="text-xs font-medium">{t('backup.categories')}</span>
 					<button class="text-xs underline" style="color: var(--color-primary);" onclick={toggleAll}>
 						{allSelected ? t('backup.deselectAll') : t('backup.selectAll')}
 					</button>
@@ -360,7 +360,7 @@
 
 			<!-- Secrets mode -->
 			<div class="mb-4">
-				<label class="block text-xs font-medium mb-2">{t('backup.secretsMode')}</label>
+				<div class="block text-xs font-medium mb-2">{t('backup.secretsMode')}</div>
 				<div class="flex flex-col gap-1.5">
 					<label class="flex items-center gap-1.5 text-xs">
 						<input type="radio" bind:group={exportSecrets} value="exclude" />
@@ -458,7 +458,7 @@
 
 				<!-- Conflict mode -->
 				<div class="mb-4">
-					<label class="block text-xs font-medium mb-2">{t('backup.conflictMode')}</label>
+					<div class="block text-xs font-medium mb-2">{t('backup.conflictMode')}</div>
 					<div class="flex flex-col gap-1.5">
 						<label class="flex items-center gap-1.5 text-xs">
 							<input type="radio" bind:group={importConflict} value="skip" />
@@ -528,8 +528,8 @@
 				{#if scheduledSettings.backup_scheduled_enabled === 'true'}
 					<div class="grid grid-cols-1 sm:grid-cols-3 gap-4">
 						<div>
-							<label class="block text-xs font-medium mb-1">{t('backup.interval')}</label>
-							<select bind:value={scheduledSettings.backup_scheduled_interval_hours}
+							<label for="backup-interval" class="block text-xs font-medium mb-1">{t('backup.interval')}</label>
+							<select id="backup-interval" bind:value={scheduledSettings.backup_scheduled_interval_hours}
 								class="w-full px-3 py-1.5 text-sm border border-[var(--color-border)] rounded-md bg-[var(--color-background)]">
 								<option value="6">6 {t('backup.hours')}</option>
 								<option value="12">12 {t('backup.hours')}</option>
@@ -540,8 +540,8 @@
 							</select>
 						</div>
 						<div>
-							<label class="block text-xs font-medium mb-1">{t('backup.secretsMode')}</label>
-							<select bind:value={scheduledSettings.backup_secrets_mode}
+							<label for="backup-secrets-mode" class="block text-xs font-medium mb-1">{t('backup.secretsMode')}</label>
+							<select id="backup-secrets-mode" bind:value={scheduledSettings.backup_secrets_mode}
 								class="w-full px-3 py-1.5 text-sm border border-[var(--color-border)] rounded-md bg-[var(--color-background)]">
 								<option value="exclude">{t('backup.secretsExclude')}</option>
 								<option value="masked">{t('backup.secretsMasked')}</option>
@@ -549,8 +549,8 @@
 							</select>
 						</div>
 						<div>
-							<label class="block text-xs font-medium mb-1">{t('backup.retention')}</label>
-							<select bind:value={scheduledSettings.backup_retention_count}
+							<label for="backup-retention" class="block text-xs font-medium mb-1">{t('backup.retention')}</label>
+							<select id="backup-retention" bind:value={scheduledSettings.backup_retention_count}
 								class="w-full px-3 py-1.5 text-sm border border-[var(--color-border)] rounded-md bg-[var(--color-background)]">
 								<option value="3">3</option>
 								<option value="5">5</option>
@@ -656,6 +656,7 @@
 		onclick={() => postRestoreModalOpen = false}
 		onkeydown={(e) => { if (e.key === 'Escape') postRestoreModalOpen = false; }}
 		role="presentation">
+		<!-- svelte-ignore a11y_click_events_have_key_events -->
 		<div role="dialog" aria-modal="true" aria-labelledby="post-restore-title" tabindex="-1"
 			style="background: var(--color-card); border: 1px solid var(--color-border); border-radius: 1rem; padding: 1.5rem; max-width: 420px; width: 100%; box-shadow: 0 20px 60px rgba(0,0,0,0.4);"
 			onclick={(e) => e.stopPropagation()}>