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.server.spec.ts

@@ -1,10 +1,8 @@
 import { beforeEach, describe, expect, it, vi } from 'vitest';
-import { actions, load } from './+page.server';
+import { load } from './+page.server';
 
 const mockApi = {
-	GET: vi.fn(),
-	POST: vi.fn(),
-	PATCH: vi.fn()
+	GET: vi.fn()
 };
 
 vi.mock('$lib/api.server', () => ({
@@ -93,37 +91,3 @@ describe('chronik/load', () => {
 		expect(invalidResult.filter).toBe('alle');
 	});
 });
-
-describe('chronik/actions', () => {
-	it('dismiss: PATCHes /api/notifications/{id}/read with the form id', async () => {
-		mockApi.PATCH.mockResolvedValue({ response: { ok: true } });
-		const formData = new FormData();
-		formData.set('id', 'n-42');
-
-		const result = await actions.dismiss({
-			request: { formData: async () => formData },
-			fetch
-		} as never);
-
-		expect(mockApi.PATCH).toHaveBeenCalledWith('/api/notifications/{id}/read', {
-			params: { path: { id: 'n-42' } }
-		});
-		expect(result).toEqual({ success: true });
-	});
-
-	it('dismiss: fails with 400 when id is missing', async () => {
-		const formData = new FormData();
-		const result = await actions.dismiss({
-			request: { formData: async () => formData },
-			fetch
-		} as never);
-		expect((result as { status: number }).status).toBe(400);
-	});
-
-	it('mark-all: POSTs /api/notifications/read-all', async () => {
-		mockApi.POST.mockResolvedValue({ response: { ok: true } });
-		const result = await actions['mark-all']({ fetch } as never);
-		expect(mockApi.POST).toHaveBeenCalledWith('/api/notifications/read-all');
-		expect(result).toEqual({ success: true });
-	});
-});