refactor(test): complete .test-host -> .test-fixture rename sweep

Round 2 renamed only MentionDropdown's fixture; three siblings retained
the old suffix. Rename PersonMentionEditor, confirm, and TranscriptionBlock
test hosts to the .test-fixture suffix and update the three importers so
the boundary is uniform across the repo. Felix #1 / Tobi #1 on PR #629.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

frontend/src/lib/document/transcription/TranscriptionBlock.svelte.spec.ts

@@ -1,7 +1,7 @@
 import { describe, it, expect, vi, afterEach } from 'vitest';
 import { cleanup, render } from 'vitest-browser-svelte';
 import { page } from 'vitest/browser';
-import TranscriptionBlockHost from './TranscriptionBlock.test-host.svelte';
+import TranscriptionBlockHost from './TranscriptionBlock.test-fixture.svelte';
 import type { ConfirmService } from '$lib/shared/services/confirm.svelte.js';
 
 afterEach(cleanup);

frontend/src/lib/shared/discussion/PersonMentionEditor.svelte.spec.ts

@@ -8,7 +8,7 @@
 import { describe, it, expect, vi, afterEach } from 'vitest';
 import { cleanup, render } from 'vitest-browser-svelte';
 import { page, userEvent } from 'vitest/browser';
-import PersonMentionEditorHost from './PersonMentionEditor.test-host.svelte';
+import PersonMentionEditorHost from './PersonMentionEditor.test-fixture.svelte';
 import type { components } from '$lib/generated/api';
 import { m } from '$lib/paraglide/messages.js';
 // Single source of truth for the debounce window — imported from the shared

frontend/src/lib/shared/services/confirm.svelte.test.ts

@@ -1,7 +1,7 @@
 import { describe, it, expect, afterEach } from 'vitest';
 import { cleanup, render } from 'vitest-browser-svelte';
 import { page, userEvent } from 'vitest/browser';
-import TestHost from './confirm.test-host.svelte';
+import TestHost from './confirm.test-fixture.svelte';
 import type { ConfirmService } from './confirm.svelte.js';
 
 afterEach(cleanup);