refactor(chronik): remove unused form actions and broken pagination UI

Two items flagged as blockers in PR #288 review:

- Markus + Sara: "Mehr laden" calls GET /api/dashboard/activity?offset=N but
  the backend's DashboardController only accepts `limit` — `offset` was
  silently ignored, and every click re-fetched the same top-40 rows. Rather
  than add backend offset/cursor support in this PR (scope creep), remove
  the Load-more UI and defer pagination to a follow-up issue. 40 items
  covers the default case; the feature can come back with proper backend
  support and its own tests.
- Markus + Sara: ?/dismiss and ?/mark-all form actions were dead code —
  the UI calls `onMarkRead` / `onMarkAllRead` callbacks (→ singleton →
  raw PATCH) and never submits either form. Delete both actions and their
  tests. Using the form-action path would require deprecating the
  NotificationBell's raw-PATCH as well — that's tracked separately as
  #286.

The Dismiss markup split from the previous commit stands on its own.

Part of #285, address PR #288 review.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

frontend/src/routes/chronik/+page.svelte

@@ -1,5 +1,5 @@
 <script lang="ts">
-import { onMount, onDestroy, tick } from 'svelte';
+import { onMount, onDestroy } from 'svelte';
 import { goto } from '$app/navigation';
 import { page } from '$app/state';
 import * as m from '$lib/paraglide/messages.js';
@@ -92,37 +92,9 @@ async function onMarkAllRead() {
 	await notificationStore.markAllRead();
 }
 
-// "Mehr laden" pagination
-let isLoadingMore = $state(false);
-let loadMoreBtn = $state<HTMLButtonElement | null>(null);
-let paginatedFeed = $state<ActivityFeedItemDTO[]>([]);
-let announcement = $state('');
-
-const mergedFeed = $derived<ActivityFeedItemDTO[]>([...data.activityFeed, ...paginatedFeed]);
-
-async function loadMore() {
-	if (isLoadingMore) return;
-	isLoadingMore = true;
-	try {
-		const res = await fetch(`/api/dashboard/activity?limit=40&offset=${mergedFeed.length}`, {
-			credentials: 'same-origin'
-		});
-		if (!res.ok) throw new Error('load failed');
-		const next = (await res.json()) as ActivityFeedItemDTO[];
-		paginatedFeed = [...paginatedFeed, ...next];
-		announcement = m.chronik_load_more_announcement({ count: next.length });
-	} catch {
-		// Keep silent in the unit path — the error card handles load failures.
-	} finally {
-		isLoadingMore = false;
-		await tick();
-		loadMoreBtn?.focus();
-	}
-}
-
 const displayFeed = $derived<ActivityFeedItemDTO[]>(
 	(() => {
-		const merged = mergedFeed;
+		const merged = data.activityFeed;
 		switch (activeFilter) {
 			case 'alle':
 				return merged;
@@ -177,32 +149,6 @@ function retry() {
 			</div>
 		{:else}
 			<ChronikTimeline items={displayFeed} />
-
-			<div aria-live="polite" class="sr-only">{announcement}</div>
-
-			<div class="mt-6 text-center">
-				<button
-					type="button"
-					bind:this={loadMoreBtn}
-					onclick={loadMore}
-					aria-busy={isLoadingMore}
-					disabled={isLoadingMore}
-					class="rounded-sm border border-line px-4 py-3 font-sans text-sm text-ink-2 transition-colors hover:bg-muted disabled:opacity-60"
-				>
-					{isLoadingMore ? m.chronik_loading() : m.chronik_load_more()}
-				</button>
-
-				{#if isLoadingMore}
-					<ul aria-hidden="true" class="mt-3 flex flex-col gap-2">
-						{#each [0, 1, 2] as i (i)}
-							<li
-								data-testid="chronik-skeleton-row"
-								class="h-[72px] rounded-sm border border-line bg-muted/40"
-							></li>
-						{/each}
-					</ul>
-				{/if}
-			</div>
 		{/if}
 	{/if}
 </main>