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/e2e/persons.spec.ts

@@ -156,7 +156,9 @@ test.describe('Person detail — sent and received documents', () => {
 			const sentHeading = page.getByRole('heading', { name: /Gesendete Dokumente/i }).locator('..');
 			const hasYearRange = await sentHeading.locator('span').filter({ hasText: /\d{4}/ }).count();
 			if (hasYearRange > 0) {
-				await expect(sentHeading.locator('span').filter({ hasText: /\d{4}/ }).first()).toBeVisible();
+				await expect(
+					sentHeading.locator('span').filter({ hasText: /\d{4}/ }).first()
+				).toBeVisible();
 				await page.screenshot({ path: 'test-results/e2e/person-year-range.png' });
 				return;
 			}
@@ -166,7 +168,9 @@ test.describe('Person detail — sent and received documents', () => {
 });
 
 test.describe('Person detail — conversations link', () => {
-	test('co-correspondent chips link to conversations pre-filled with both persons', async ({ page }) => {
+	test('co-correspondent chips link to conversations pre-filled with both persons', async ({
+		page
+	}) => {
 		await page.goto('/persons');
 		const firstLink = page.locator('a[href^="/persons/"]:not([href="/persons/new"])').first();
 		const href = await firstLink.getAttribute('href');
@@ -176,7 +180,7 @@ test.describe('Person detail — conversations link', () => {
 
 		// Co-correspondent chips link to /conversations?senderId=X&receiverId=Y
 		const chip = page.locator(`a[href^="/conversations?senderId=${personId}&receiverId="]`).first();
-		if (await chip.count() > 0) {
+		if ((await chip.count()) > 0) {
 			const chipHref = await chip.getAttribute('href');
 			expect(chipHref).toMatch(/\/conversations\?senderId=.+&receiverId=.+/);
 		}