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/actions/doubletap.ts

@@ -20,8 +20,8 @@ export interface DoubletapOptions {
 }
 
 interface DoubletapAttributes {
-	'ondoubletap'?: (event: CustomEvent<void>) => void;
-	'onsingletap'?: (event: CustomEvent<void>) => void;
+	ondoubletap?: (event: CustomEvent<void>) => void;
+	onsingletap?: (event: CustomEvent<void>) => void;
 }
 
 export function doubletap(

frontend/src/lib/actions/focus-trap.ts

@@ -30,7 +30,9 @@ export function focusTrap(
 	options: FocusTrapOptions = {}
 ): ActionReturn<FocusTrapOptions> {
 	let opts = options;
-	const previouslyFocused = (typeof document !== 'undefined' ? document.activeElement : null) as HTMLElement | null;
+	const previouslyFocused = (
+		typeof document !== 'undefined' ? document.activeElement : null
+	) as HTMLElement | null;
 
 	function onKeyDown(e: KeyboardEvent) {
 		if (e.key === 'Escape' && opts.closeOnEscape !== false && opts.onclose) {
@@ -85,7 +87,11 @@ export function focusTrap(
 		destroy() {
 			node.removeEventListener('keydown', onKeyDown);
 			if (previouslyFocused && typeof previouslyFocused.focus === 'function') {
-				try { previouslyFocused.focus({ preventScroll: true }); } catch { /* element may have unmounted */ }
+				try {
+					previouslyFocused.focus({ preventScroll: true });
+				} catch {
+					/* element may have unmounted */
+				}
 			}
 		}
 	};

frontend/src/lib/actions/longpress.ts

@@ -24,7 +24,7 @@ export interface LongpressOptions {
 }
 
 interface LongpressAttributes {
-	'onlongpress'?: (event: CustomEvent<void>) => void;
+	onlongpress?: (event: CustomEvent<void>) => void;
 }
 
 export function longpress(

frontend/src/lib/actions/scroll-lock.ts

@@ -40,7 +40,7 @@ function unlock() {
  * dialog is open (e.g. inside `{#if open}` or alongside a `class:` toggle) so the
  * action's create/destroy line up with open/close.
  */
-export function scrollLock(node: HTMLElement): ActionReturn {
+export function scrollLock(_node: HTMLElement): ActionReturn {
 	lock();
 	return {
 		destroy() {