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/login/+page.server.ts

@@ -3,47 +3,47 @@ import { env } from '$env/dynamic/private';
 import { getErrorMessage } from '$lib/errors';
 
 export const actions = {
-    login: async ({ request, cookies, fetch }) => {
-        const data = await request.formData();
-        const username = data.get('username') as string;
-        const password = data.get('password') as string;
+	login: async ({ request, cookies, fetch }) => {
+		const data = await request.formData();
+		const username = data.get('username') as string;
+		const password = data.get('password') as string;
 
-        if (!username || !password) {
-            return fail(400, { error: 'Bitte Benutzername und Passwort eingeben.' });
-        }
+		if (!username || !password) {
+			return fail(400, { error: 'Bitte Benutzername und Passwort eingeben.' });
+		}
 
-        const credentials = btoa(`${username}:${password}`);
-        const authHeader = `Basic ${credentials}`;
+		const credentials = btoa(`${username}:${password}`);
+		const authHeader = `Basic ${credentials}`;
 
-        // Raw fetch is intentional here: we need to pass an explicit Authorization
-        // header built from the form data, not the cookie-based auth used elsewhere.
-        try {
-            const baseUrl = env.API_INTERNAL_URL || 'http://localhost:8080';
-            const response = await fetch(`${baseUrl}/api/users/me`, {
-                method: 'GET',
-                headers: { Authorization: authHeader }
-            });
+		// Raw fetch is intentional here: we need to pass an explicit Authorization
+		// header built from the form data, not the cookie-based auth used elsewhere.
+		try {
+			const baseUrl = env.API_INTERNAL_URL || 'http://localhost:8080';
+			const response = await fetch(`${baseUrl}/api/users/me`, {
+				method: 'GET',
+				headers: { Authorization: authHeader }
+			});
 
-            if (response.status === 401 || response.status === 403) {
-                return fail(401, { error: getErrorMessage('UNAUTHORIZED') });
-            }
+			if (response.status === 401 || response.status === 403) {
+				return fail(401, { error: getErrorMessage('UNAUTHORIZED') });
+			}
 
-            if (!response.ok) {
-                return fail(500, { error: getErrorMessage('INTERNAL_ERROR') });
-            }
+			if (!response.ok) {
+				return fail(500, { error: getErrorMessage('INTERNAL_ERROR') });
+			}
 
-            cookies.set('auth_token', authHeader, {
-                path: '/',
-                httpOnly: true,
-                sameSite: 'strict',
-                secure: false, // set to true when HTTPS is available
-                maxAge: 60 * 60 * 24
-            });
-        } catch (e) {
-            console.error(e);
-            return fail(500, { error: getErrorMessage('INTERNAL_ERROR') });
-        }
+			cookies.set('auth_token', authHeader, {
+				path: '/',
+				httpOnly: true,
+				sameSite: 'strict',
+				secure: false, // set to true when HTTPS is available
+				maxAge: 60 * 60 * 24
+			});
+		} catch (e) {
+			console.error(e);
+			return fail(500, { error: getErrorMessage('INTERNAL_ERROR') });
+		}
 
-        return redirect(303, '/');
-    }
+		return redirect(303, '/');
+	}
 } satisfies Actions;