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/SearchPalette.svelte

@@ -26,7 +26,9 @@
 	let query = $state('');
 	let activeIndex = $state(0);
 	let loading = $state(false);
-	let inputEl: HTMLInputElement;
+	let inputEl = $state<HTMLInputElement | undefined>();
+	const listboxId = 'sp-listbox';
+	const optionId = (idx: number) => `sp-option-${idx}`;
 
 	// Expose openPalette to parent via callback
 	$effect(() => { onopen?.(openPalette); });
@@ -206,7 +208,7 @@
 
 {#if open}
 	<!-- Backdrop -->
-	<div class="sp-backdrop" onclick={closePalette} role="presentation"></div>
+	<div class="sp-backdrop" onclick={closePalette} onkeydown={(e) => { if (e.key === 'Escape') closePalette(); }} role="button" tabindex="-1" aria-label={t('searchPalette.close')}></div>
 
 	<!-- Palette -->
 	<div class="sp-container">
@@ -218,11 +220,16 @@
 				placeholder={t('searchPalette.placeholder')}
 				class="sp-input"
 				type="text"
+				role="combobox"
+				aria-expanded={flatResults.length > 0}
+				aria-controls={listboxId}
+				aria-activedescendant={flatResults.length > 0 ? optionId(activeIndex) : undefined}
+				aria-autocomplete="list"
 			/>
 			<kbd class="sp-kbd">ESC</kbd>
 		</div>
 
-		<div class="sp-results">
+		<div class="sp-results" id={listboxId} role="listbox">
 			{#if loading}
 				<div class="sp-empty">
 					<div class="w-4 h-4 rounded-full border-2 border-[var(--color-primary)] border-t-transparent animate-spin"></div>
@@ -239,9 +246,12 @@
 						<MdiIcon name={group.icon} size={14} />
 						{group.label}
 					</div>
-					{#each group.items as item, i}
+					{#each group.items as item}
 						{@const flatIdx = flatIndexMap.get(item) ?? -1}
 						<button
+							id={optionId(flatIdx)}
+							role="option"
+							aria-selected={flatIdx === activeIndex}
 							class="sp-item"
 							class:sp-active={flatIdx === activeIndex}
 							onclick={() => navigateTo(item)}