fix(transcription): replace broken HTML5 drag with pointer-based drag

HTML5 drag-and-drop didn't work — the grip handle couldn't initiate
drag properly. Replace with pointer event-based drag:

- Grip handle pointerdown starts drag, captures pointer
- Pointermove tracks offset, shows floaty style (shadow, scale, ring)
- Turquoise drop indicator line appears between blocks at cursor position
- Pointerup finalizes: reorders array and calls PUT /reorder endpoint

Visual feedback:
- Dragged block: shadow-xl, ring-2 ring-turquoise/40, scale 1.02, opacity 0.9
- Drop indicator: turquoise h-1 rounded bar between blocks

6 new TranscriptionEditView tests:
- renders blocks in sort order
- shows next-block CTA
- shows empty state
- move-up disabled on first block
- move-down disabled on last block
- drag handle present on each block

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

frontend/src/lib/components/TranscriptionEditView.svelte

@@ -160,45 +160,63 @@ function handleMoveDown(blockId: string) {
 	reorder(sorted.map((b) => b.id));
 }
 
-// ── Drag and drop ────────────────────────────────────────────────────────
+// ── Pointer-based drag and drop ──────────────────────────────────────────
 
 let draggedBlockId: string | null = $state(null);
+let dropTargetIdx: number | null = $state(null);
+let dragOffsetY: number = $state(0);
+let dragStartY = 0;
+let capturedEl: HTMLElement | null = null;
+let listEl: HTMLElement | null = null;
 
-function handleDragStart(e: DragEvent, blockId: string) {
-	if (!(e.target as HTMLElement).closest('[data-drag-handle]')) {
-		e.preventDefault();
-		return;
-	}
+function handleGripDown(e: PointerEvent, blockId: string) {
+	if (!(e.target as HTMLElement).closest('[data-drag-handle]')) return;
+	e.preventDefault();
 	draggedBlockId = blockId;
-	e.dataTransfer!.effectAllowed = 'move';
+	dragStartY = e.clientY;
+	dragOffsetY = 0;
+	capturedEl = (e.target as HTMLElement).closest('[data-block-wrapper]') as HTMLElement;
+	capturedEl?.setPointerCapture(e.pointerId);
 }
 
-function handleDragOver(e: DragEvent) {
-	e.preventDefault();
-	e.dataTransfer!.dropEffect = 'move';
-}
+function handlePointerMove(e: PointerEvent) {
+	if (!draggedBlockId || !listEl) return;
+	dragOffsetY = e.clientY - dragStartY;
 
-function handleDrop(e: DragEvent, targetBlockId: string) {
-	e.preventDefault();
-	if (!draggedBlockId || draggedBlockId === targetBlockId) {
-		draggedBlockId = null;
-		return;
+	const wrappers = Array.from(listEl.querySelectorAll('[data-block-wrapper]'));
+	const dragIdx = sortedBlocks.findIndex((b) => b.id === draggedBlockId);
+	let target: number | null = null;
+
+	for (let i = 0; i < wrappers.length; i++) {
+		const rect = wrappers[i].getBoundingClientRect();
+		if (e.clientY < rect.top + rect.height / 2) {
+			target = i;
+			break;
+		}
 	}
-	const sorted = [...sortedBlocks];
-	const fromIdx = sorted.findIndex((b) => b.id === draggedBlockId);
-	const toIdx = sorted.findIndex((b) => b.id === targetBlockId);
-	if (fromIdx < 0 || toIdx < 0) {
-		draggedBlockId = null;
-		return;
-	}
-	const [moved] = sorted.splice(fromIdx, 1);
-	sorted.splice(toIdx, 0, moved);
-	draggedBlockId = null;
-	reorder(sorted.map((b) => b.id));
+	if (target === null) target = wrappers.length;
+	if (target === dragIdx || target === dragIdx + 1) target = null;
+	dropTargetIdx = target;
 }
 
-function handleDragEnd() {
+function handlePointerUp() {
+	if (!draggedBlockId) return;
+
+	if (dropTargetIdx !== null) {
+		const sorted = [...sortedBlocks];
+		const fromIdx = sorted.findIndex((b) => b.id === draggedBlockId);
+		if (fromIdx >= 0) {
+			const [moved] = sorted.splice(fromIdx, 1);
+			const insertAt = dropTargetIdx > fromIdx ? dropTargetIdx - 1 : dropTargetIdx;
+			sorted.splice(insertAt, 0, moved);
+			reorder(sorted.map((b) => b.id));
+		}
+	}
+
 	draggedBlockId = null;
+	dropTargetIdx = null;
+	dragOffsetY = 0;
+	capturedEl = null;
 }
 
 function flushViaBeacon() {
@@ -229,17 +247,24 @@ $effect(() => {
 
 <div class="flex h-full flex-col overflow-y-auto bg-surface p-4">
 	{#if hasBlocks}
-		<div class="flex flex-col gap-3">
+		<!-- svelte-ignore a11y_no_static_element_interactions -->
+		<div
+			class="flex flex-col gap-3"
+			bind:this={listEl}
+			onpointermove={handlePointerMove}
+			onpointerup={handlePointerUp}
+		>
 			{#each sortedBlocks as block, i (block.id)}
+				{#if dropTargetIdx === i}
+					<div class="h-1 rounded-full bg-turquoise transition-all"></div>
+				{/if}
 				<!-- svelte-ignore a11y_no_static_element_interactions -->
 				<div
+					data-block-wrapper
 					onblur={handleBlur}
-					draggable={true}
-					ondragstart={(e) => handleDragStart(e, block.id)}
-					ondragover={handleDragOver}
-					ondrop={(e) => handleDrop(e, block.id)}
-					ondragend={handleDragEnd}
-					class={draggedBlockId === block.id ? 'opacity-40' : ''}
+					onpointerdown={(e) => handleGripDown(e, block.id)}
+					class="relative transition-all duration-150 {draggedBlockId === block.id ? 'z-10 rounded-lg shadow-xl ring-2 ring-turquoise/40' : ''}"
+					style={draggedBlockId === block.id ? `transform: translateY(${dragOffsetY}px) scale(1.02); opacity: 0.9;` : ''}
 				>
 					<TranscriptionBlock
 						blockId={block.id}
@@ -263,6 +288,10 @@ $effect(() => {
 				</div>
 			{/each}
 
+			{#if dropTargetIdx === sortedBlocks.length}
+				<div class="h-1 rounded-full bg-turquoise transition-all"></div>
+			{/if}
+
 			<!-- Next block CTA — dashed outline hint -->
 			<div
 				class="flex items-center justify-center rounded border border-dashed border-line px-4 py-5 text-center font-sans text-sm text-ink-3"

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

@@ -0,0 +1,78 @@
+import { describe, it, expect, vi, afterEach } from 'vitest';
+import { cleanup, render } from 'vitest-browser-svelte';
+import { page } from 'vitest/browser';
+import TranscriptionEditView from './TranscriptionEditView.svelte';
+
+afterEach(cleanup);
+
+const block1 = {
+	id: 'b1',
+	annotationId: 'a1',
+	documentId: 'doc-1',
+	text: 'Block eins',
+	label: null,
+	sortOrder: 0,
+	version: 0
+};
+const block2 = {
+	id: 'b2',
+	annotationId: 'a2',
+	documentId: 'doc-1',
+	text: 'Block zwei',
+	label: null,
+	sortOrder: 1,
+	version: 0
+};
+
+function renderView(overrides: Record<string, unknown> = {}) {
+	return render(TranscriptionEditView, {
+		documentId: 'doc-1',
+		blocks: [block1, block2],
+		canComment: true,
+		currentUserId: 'user-1',
+		onBlockFocus: vi.fn(),
+		onSaveBlock: vi.fn(),
+		onDeleteBlock: vi.fn(),
+		...overrides
+	});
+}
+
+describe('TranscriptionEditView — rendering', () => {
+	it('renders blocks in sort order', async () => {
+		renderView();
+		const textareas = page.getByRole('textbox').all();
+		expect(textareas.length).toBeGreaterThanOrEqual(2);
+	});
+
+	it('shows next-block CTA after block list', async () => {
+		renderView();
+		await expect.element(page.getByText(/Block 3/)).toBeInTheDocument();
+	});
+
+	it('shows empty state when no blocks', async () => {
+		renderView({ blocks: [] });
+		await expect.element(page.getByText(/Markiere einen Bereich/)).toBeInTheDocument();
+	});
+});
+
+describe('TranscriptionEditView — reorder', () => {
+	it('renders move-up button disabled on first block', async () => {
+		renderView();
+		const upButtons = page.getByRole('button', { name: 'Nach oben' }).all();
+		// First block's up button should be disabled
+		await expect.element(upButtons[0]).toBeDisabled();
+	});
+
+	it('renders move-down button disabled on last block', async () => {
+		renderView();
+		const downButtons = page.getByRole('button', { name: 'Nach unten' }).all();
+		// Last block's down button should be disabled
+		await expect.element(downButtons[downButtons.length - 1]).toBeDisabled();
+	});
+
+	it('has a drag handle on each block', async () => {
+		renderView();
+		const handles = document.querySelectorAll('[data-drag-handle]');
+		expect(handles.length).toBe(2);
+	});
+});