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/Hint.svelte

@@ -4,7 +4,8 @@
 	let { text = '' } = $props<{ text: string }>();
 	let visible = $state(false);
 	let tooltipStyle = $state('');
-	let btnEl: HTMLButtonElement;
+	let btnEl = $state<HTMLButtonElement | undefined>();
+	const tooltipId = `hint-${Math.random().toString(36).slice(2, 9)}`;
 
 	function show() {
 		if (!btnEl) return;
@@ -14,7 +15,7 @@
 		let left = rect.left + rect.width / 2 - tooltipWidth / 2;
 		if (left < 8) left = 8;
 		if (left + tooltipWidth > window.innerWidth - 8) left = window.innerWidth - tooltipWidth - 8;
-		tooltipStyle = `position:fixed; z-index:99999; bottom:${window.innerHeight - rect.top + 8}px; left:${left}px; width:${tooltipWidth}px;`;
+		tooltipStyle = `position:fixed; z-index:9999; bottom:${window.innerHeight - rect.top + 8}px; left:${left}px; width:${tooltipWidth}px;`;
 	}
 
 	function hide() {
@@ -31,13 +32,14 @@
 	onfocus={show}
 	onblur={hide}
 	aria-label={text}
+	aria-describedby={visible ? tooltipId : undefined}
 	title={text}
 	tabindex="0"
 >?</button>
 
 {#if visible}
 	<div use:portal>
-		<div role="tooltip" style={tooltipStyle} class="hint-tooltip">
+		<div id={tooltipId} role="tooltip" style={tooltipStyle} class="hint-tooltip">
 			{text}
 		</div>
 	</div>