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/persons/+page.svelte

@@ -26,13 +26,18 @@ function handleSearch(e: Event) {
 				{m.persons_subtitle()}
 			</p>
 			{#if data.canWrite}
-			<a
-				href="/persons/new"
-				class="mt-3 inline-flex items-center gap-1 text-sm font-medium text-brand-navy/60 transition-colors hover:text-brand-navy"
-			>
-				<img src="/degruyter-icons/Simple/Medium-24px/SVG/Action/Add/Add-General-MD.svg" alt="" aria-hidden="true" class="h-4 w-4" />
-				{m.persons_btn_new()}
-			</a>
+				<a
+					href="/persons/new"
+					class="mt-3 inline-flex items-center gap-1 text-sm font-medium text-brand-navy/60 transition-colors hover:text-brand-navy"
+				>
+					<img
+						src="/degruyter-icons/Simple/Medium-24px/SVG/Action/Add/Add-General-MD.svg"
+						alt=""
+						aria-hidden="true"
+						class="h-4 w-4"
+					/>
+					{m.persons_btn_new()}
+				</a>
 			{/if}
 		</div>
 
@@ -51,7 +56,12 @@ function handleSearch(e: Event) {
 				<div
 					class="pointer-events-none absolute inset-y-0 right-0 flex items-center pr-3 text-gray-400"
 				>
-					<img src="/degruyter-icons/Simple/Medium-24px/SVG/Action/Mag-Glass-MD.svg" alt="" aria-hidden="true" class="h-4 w-4 opacity-40" />
+					<img
+						src="/degruyter-icons/Simple/Medium-24px/SVG/Action/Mag-Glass-MD.svg"
+						alt=""
+						aria-hidden="true"
+						class="h-4 w-4 opacity-40"
+					/>
 				</div>
 			</div>
 		</div>
@@ -64,14 +74,19 @@ function handleSearch(e: Event) {
 			<div
 				class="mb-3 flex h-12 w-12 items-center justify-center rounded-full bg-brand-sand/30 text-brand-navy"
 			>
-				<img src="/degruyter-icons/Simple/Medium-24px/SVG/Action/Account-MD.svg" alt="" aria-hidden="true" class="h-6 w-6" />
+				<img
+					src="/degruyter-icons/Simple/Medium-24px/SVG/Action/Account-MD.svg"
+					alt=""
+					aria-hidden="true"
+					class="h-6 w-6"
+				/>
 			</div>
 			<p class="font-serif text-lg text-brand-navy">{m.persons_empty_heading()}</p>
 			<p class="mt-1 font-sans text-sm text-gray-500">{m.persons_empty_text()}</p>
 		</div>
 	{:else}
 		<div class="grid grid-cols-1 gap-6 sm:grid-cols-2 md:grid-cols-3 lg:grid-cols-4">
-			{#each data.persons as person}
+			{#each data.persons as person (person.id)}
 				<a href="/persons/{person.id}" class="group block h-full">
 					<div
 						class="relative flex h-full items-center gap-4 overflow-hidden rounded border border-brand-sand bg-white p-6 shadow-sm transition-all duration-200 hover:border-brand-navy hover:shadow-md"