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/routes/recover/+page.svelte

@@ -101,7 +101,9 @@
 	}
 </script>
 
-<div class="flex min-h-screen flex-col bg-gray-50 px-4 pt-[env(safe-area-inset-top)] dark:bg-gray-950">
+<div
+	class="flex min-h-screen flex-col bg-gray-50 px-4 pt-[env(safe-area-inset-top)] dark:bg-gray-950"
+>
 	<div class="-mx-4 flex items-center px-2 py-3">
 		<IconButton label="Zurück" onclick={goBack} data-testid="recover-back">
 			<svg class="h-5 w-5" fill="none" viewBox="0 0 24 24" stroke="currentColor" stroke-width="2">
@@ -110,10 +112,19 @@
 		</IconButton>
 	</div>
 	<div class="m-auto w-full max-w-sm">
-		<h1 class="mb-2 text-center text-2xl font-bold text-gray-900 dark:text-gray-100">Konto wiederherstellen</h1>
-		<p class="mb-6 text-center text-gray-600 dark:text-gray-400">Gib deinen Namen und deinen PIN ein.</p>
+		<h1 class="mb-2 text-center text-2xl font-bold text-gray-900 dark:text-gray-100">
+			Konto wiederherstellen
+		</h1>
+		<p class="mb-6 text-center text-gray-600 dark:text-gray-400">
+			Gib deinen Namen und deinen PIN ein.
+		</p>
 
-		<form onsubmit={(e) => { e.preventDefault(); handleRecover(); }}>
+		<form
+			onsubmit={(e) => {
+				e.preventDefault();
+				handleRecover();
+			}}
+		>
 			<input
 				type="text"
 				bind:value={displayName}
@@ -135,7 +146,9 @@
 			/>
 
 			{#if error}
-				<p class="mb-3 text-sm text-red-600 dark:text-red-400" data-testid="recover-error">{error}</p>
+				<p class="mb-3 text-sm text-red-600 dark:text-red-400" data-testid="recover-error">
+					{error}
+				</p>
 			{/if}
 
 			<button
@@ -151,8 +164,12 @@
 		<!-- PIN lost entirely (never noted, or reset by a host while offline): a soft dead-end
 		     without this — offer the host-reset request path. -->
 		{#if pinRequestSent}
-			<p class="mt-4 text-center text-sm text-green-700 dark:text-green-400" data-testid="recover-pin-request-sent">
-				Anfrage gesendet. Bitte einen Host, deine PIN zurückzusetzen — komm danach mit der neuen PIN zurück.
+			<p
+				class="mt-4 text-center text-sm text-green-700 dark:text-green-400"
+				data-testid="recover-pin-request-sent"
+			>
+				Anfrage gesendet. Bitte einen Host, deine PIN zurückzusetzen — komm danach mit der neuen PIN
+				zurück.
 			</p>
 		{:else}
 			<button