fix(transcription): always show comment list, compose box on demand

Comments were only visible after clicking "Kommentieren". Now:
- Comment list always renders (CommentThread with loadOnMount=true)
- Compose box hidden by default (showCompose prop on CommentThread)
- Clicking "Kommentieren" sets commentOpen=true → shows compose box
- Closing hides compose box but comments remain visible

This separates "viewing comments" (always) from "writing a comment"
(on demand via Kommentieren button).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/lib/components/TranscriptionBlock.svelte.spec.ts

@@ -16,7 +16,6 @@ function renderBlock(overrides: Record<string, unknown> = {}) {
 		saveState: 'idle' as const,
 		canComment: true,
 		currentUserId: 'user-1',
-		commentCount: 0,
 		onTextChange: vi.fn(),
 		onFocus: vi.fn(),
 		onDeleteClick: vi.fn(),