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/Modal.svelte

@@ -1,5 +1,4 @@
 <script lang="ts">
-	import { onMount } from 'svelte';
 	import MdiIcon from './MdiIcon.svelte';
 	import { t } from '$lib/i18n';
 	import { portal } from '$lib/portal';
@@ -12,7 +11,7 @@
 	}>();
 
 	let visible = $state(false);
-	let panelEl: HTMLDivElement;
+	let panelEl = $state<HTMLDivElement | undefined>();
 	let previouslyFocused: HTMLElement | null = null;
 
 	const uniqueId = `modal-${Math.random().toString(36).slice(2, 9)}`;
@@ -81,13 +80,17 @@
 			class:visible
 			onclick={onclose}
 			onkeydown={handleBackdropKeydown}
-			role="presentation"
+			role="button"
+			tabindex="-1"
+			aria-label={t('common.close')}
 		>
+			<!-- svelte-ignore a11y_click_events_have_key_events -->
 			<div
 				bind:this={panelEl}
 				class="modal-panel"
 				class:visible
 				role="dialog"
+				tabindex="-1"
 				aria-modal="true"
 				aria-labelledby="modal-title-{uniqueId}"
 				onclick={(e) => e.stopPropagation()}
@@ -195,8 +198,8 @@
 		display: flex;
 		align-items: center;
 		justify-content: center;
-		width: 2.1rem;
-		height: 2.1rem;
+		width: 2.5rem;
+		height: 2.5rem;
 		border-radius: 10px;
 		border: 1px solid transparent;
 		background: transparent;