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/routes/api/documents/[id]/file/+server.ts

@@ -2,18 +2,18 @@ import type { RequestHandler } from './$types';
 import { env } from 'process';
 
 export const GET: RequestHandler = async ({ params, fetch }) => {
-    const backendUrl = `${env.API_INTERNAL_URL || 'http://localhost:8080'}/api/documents/${params.id}/file`;
+	const backendUrl = `${env.API_INTERNAL_URL || 'http://localhost:8080'}/api/documents/${params.id}/file`;
 
-    const response = await fetch(backendUrl);
+	const response = await fetch(backendUrl);
 
-    if (!response.ok) {
-        return new Response(null, { status: response.status });
-    }
+	if (!response.ok) {
+		return new Response(null, { status: response.status });
+	}
 
-    return new Response(response.body, {
-        headers: {
-            'Content-Type': response.headers.get('Content-Type') ?? 'application/octet-stream',
-            'Content-Disposition': response.headers.get('Content-Disposition') ?? ''
-        }
-    });
+	return new Response(response.body, {
+		headers: {
+			'Content-Type': response.headers.get('Content-Type') ?? 'application/octet-stream',
+			'Content-Disposition': response.headers.get('Content-Disposition') ?? ''
+		}
+	});
 };