fix(frontend): enforce lint locally and in CI, fix all pre-existing violations

## Pre-commit hook
- Add .husky/pre-commit at repo root: runs `cd frontend && npm run lint`
- Update prepare script in package.json to auto-configure git hooks path
  on npm install (git -C .. config core.hooksPath .husky)
- Add lint step to CI unit-tests job so it catches issues before tests run
- Add generated dirs to .prettierignore (paraglide_bak*, test-results, .auth)
- Add src/lib/paraglide_bak* to .gitignore so ESLint can ignore them

## ESLint fixes (all pre-existing)
- Disable svelte/no-navigation-without-resolve: false positive in SvelteKit
  (rule targets Svelte 5 standalone routing, not SvelteKit <a href>)
- Fix svelte/require-each-key: add (item.id)/(item) keys to all {#each} blocks
  across 10 files — improves Svelte reconciliation performance
- Fix svelte/prefer-writable-derived in PersonTypeahead: $state+$effect → $derived
- Fix svelte/prefer-svelte-reactivity: URLSearchParams → SvelteURLSearchParams,
  Map → SvelteMap (enables Svelte reactive tracking)
- Fix @typescript-eslint/no-unused-vars: remove dead imports/variables

## Prettier
- Run npm run format to bring all source files in line with .prettierrc

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/lib/utils/date.ts

@@ -3,9 +3,9 @@
  * Uses T12:00:00 to avoid UTC timezone off-by-one when converting to local time.
  */
 export function formatDate(isoDate: string): string {
-    return new Intl.DateTimeFormat('de-DE', {
-        day: 'numeric',
-        month: 'long',
-        year: 'numeric'
-    }).format(new Date(isoDate + 'T12:00:00'));
+	return new Intl.DateTimeFormat('de-DE', {
+		day: 'numeric',
+		month: 'long',
+		year: 'numeric'
+	}).format(new Date(isoDate + 'T12:00:00'));
 }

frontend/src/lib/utils/sort.spec.ts

@@ -2,7 +2,7 @@ import { describe, expect, it } from 'vitest';
 import { sortDocumentsByDate } from './sort';
 
 const doc = (id: string, documentDate: string | null) =>
-	({ id, documentDate } as { id: string; documentDate: string | null });
+	({ id, documentDate }) as { id: string; documentDate: string | null };
 
 describe('sortDocumentsByDate', () => {
 	it('sorts DESC by default — newest first', () => {