chore(frontend): add ESLint + Prettier; fix real findings; format the tree

The frontend had no JS/TS linter — only svelte-check. Add flat-config ESLint (typescript-eslint
+ eslint-plugin-svelte) and Prettier (tabs/single-quote, matching the existing style).

Rules encode "catch bugs, not enforce taste":
  - svelte/require-each-key KEPT — it is the exact bug class as the feed mis-tap fix. Fixed every
    flagged block: keyed activeFilters, filteredUsers, stagedFiles (by previewUrl), captionTags,
    admin tabs/jobs/users, the export-viewer suggestions/filters/comments, and the static skeleton
    loops.
  - svelte/prefer-svelte-reactivity KEPT — inline-disabled only the verified-safe sites (a local
    freq Map in a $derived.by, throwaway URLSearchParams query builders), with a reason each.
  - svelte/no-navigation-without-resolve OFF — wants resolve() around every goto()/href; taste, not
    a bug, and pure churn.
  - svelte/no-unused-svelte-ignore OFF — those comments are consumed by svelte-check, which ESLint
    can't see, so it wrongly calls them unused; removing them would reintroduce a11y warnings.
  - no-explicit-any OFF for *.test.ts only (partial fixtures legitimately use any).

Real code fixes beyond keys: removed a dead jobLabel(), an unused ViewerComment import and unused
catch binding, an unused scroll-lock arg, and replaced an empty interface with a type alias.

Then `prettier --write` (54 files). Formatting only. Verified: eslint clean, svelte-check 0 errors,
vitest 46 passed, vite build succeeds.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

frontend/src/lib/diashow/queue.ts

@@ -46,9 +46,7 @@ export class SlideQueue {
 		// 2. Refill shuffle queue from `allKnown` minus recently shown.
 		if (this.shuffleQueue.length === 0) {
 			this.shuffleQueue = shuffle(
-				Array.from(this.allKnown.values()).filter(
-					(s) => !this.recentlyShown.includes(s.id)
-				)
+				Array.from(this.allKnown.values()).filter((s) => !this.recentlyShown.includes(s.id))
 			);
 			// If everything is recently shown (small event), fall back to the full pool.
 			if (this.shuffleQueue.length === 0) {

frontend/src/lib/diashow/transitions/crossfade.svelte

@@ -20,14 +20,7 @@
 >
 	{#if isVideo}
 		<!-- svelte-ignore a11y_media_has_caption -->
-		<video
-			{src}
-			autoplay
-			muted
-			playsinline
-			{onended}
-			class="h-full w-full object-contain"
-		></video>
+		<video {src} autoplay muted playsinline {onended} class="h-full w-full object-contain"></video>
 	{:else}
 		<img {src} alt="" class="h-full w-full object-contain" />
 	{/if}
@@ -35,7 +28,11 @@
 
 <style>
 	@keyframes crossfade-in {
-		from { opacity: 0; }
-		to   { opacity: 1; }
+		from {
+			opacity: 0;
+		}
+		to {
+			opacity: 1;
+		}
 	}
 </style>

frontend/src/lib/diashow/transitions/kenburns.svelte

@@ -24,14 +24,7 @@
 >
 	{#if isVideo}
 		<!-- svelte-ignore a11y_media_has_caption -->
-		<video
-			{src}
-			autoplay
-			muted
-			playsinline
-			{onended}
-			class="h-full w-full object-contain"
-		></video>
+		<video {src} autoplay muted playsinline {onended} class="h-full w-full object-contain"></video>
 	{:else}
 		<img
 			{src}
@@ -44,11 +37,19 @@
 
 <style>
 	@keyframes kb-fade {
-		from { opacity: 0; }
-		to   { opacity: 1; }
+		from {
+			opacity: 0;
+		}
+		to {
+			opacity: 1;
+		}
 	}
 	@keyframes kb-zoom {
-		from { transform: scale(1.0); }
-		to   { transform: scale(1.1); }
+		from {
+			transform: scale(1);
+		}
+		to {
+			transform: scale(1.1);
+		}
 	}
 </style>

frontend/src/lib/diashow/wakelock.ts

@@ -13,7 +13,9 @@ let sentinel: SentinelLike | null = null;
 let visibilityHandler: (() => void) | null = null;
 
 export async function acquireWakeLock(): Promise<void> {
-	const wakeLock = (navigator as Navigator & { wakeLock?: { request: (t: string) => Promise<SentinelLike> } }).wakeLock;
+	const wakeLock = (
+		navigator as Navigator & { wakeLock?: { request: (t: string) => Promise<SentinelLike> } }
+	).wakeLock;
 	if (!wakeLock) return;
 	try {
 		sentinel = await wakeLock.request('screen');