feat(ui): manual-first OCR workflow — remove full-page auto-segmentation

Drawing annotations is now the primary workflow. OCR only runs on
manually drawn regions (guided mode always). Full-page layout detection
and the useExistingAnnotations checkbox are removed entirely.

- OcrTrigger: guided-only, disabled with hint when no annotations exist
- TranscriptionEditView: empty state shows draw-regions instruction,
  OCR trigger moved out of collapsible and shown inline after block list
- i18n: add ocr_trigger_no_annotations, ocr_section_heading,
  transcription_empty_draw_hint; remove ocr_use_existing_annotations keys

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

frontend/src/lib/components/OcrTrigger.svelte

@@ -1,67 +1,38 @@
 <script lang="ts">
-import { untrack } from 'svelte';
 import { m } from '$lib/paraglide/messages.js';
-import { getConfirmService } from '$lib/services/confirm.svelte';
 import ScriptTypeSelect from './ScriptTypeSelect.svelte';
 
 interface Props {
-	existingBlockCount: number;
+	blockCount: number;
 	storedScriptType: string;
-	annotationCount?: number;
 	onTrigger: (scriptType: string, useExistingAnnotations: boolean) => void;
 }
 
-let { existingBlockCount, storedScriptType, annotationCount = 0, onTrigger }: Props = $props();
-
-const { confirm } = getConfirmService();
+let { blockCount, storedScriptType, onTrigger }: Props = $props();
 
+import { untrack } from 'svelte';
 let selectedScriptType: string = $state(
 	untrack(() => (storedScriptType && storedScriptType !== 'UNKNOWN' ? storedScriptType : ''))
 );
 
-let useExistingAnnotations: boolean = $state(false);
-
-async function handleClick() {
+function handleClick() {
 	if (!selectedScriptType) return;
-
-	if (!useExistingAnnotations && existingBlockCount > 0) {
-		const confirmed = await confirm({
-			title: m.ocr_confirm_title(),
-			body: m.ocr_confirm_body({ count: String(existingBlockCount) }),
-			confirmLabel: m.ocr_confirm_btn(),
-			destructive: true
-		});
-		if (!confirmed) return;
-	}
-
-	onTrigger(selectedScriptType, useExistingAnnotations);
+	onTrigger(selectedScriptType, true);
 }
 </script>
 
 <div class="flex flex-col gap-3">
 	<ScriptTypeSelect bind:value={selectedScriptType} />
-	{#if annotationCount > 0}
-		<div class="flex flex-col gap-1">
-			<label class="flex cursor-pointer items-center gap-2">
-				<input
-					type="checkbox"
-					bind:checked={useExistingAnnotations}
-					class="h-4 w-4 cursor-pointer rounded-sm border-brand-navy/30 accent-brand-navy"
-				/>
-				<span class="font-sans text-sm font-medium text-brand-navy">
-					{m.ocr_use_existing_annotations()}
-				</span>
-			</label>
-			<p class="pl-6 text-xs text-ink-3">{m.ocr_use_existing_annotations_hint()}</p>
-		</div>
-	{/if}
 	<button
 		type="button"
-		disabled={!selectedScriptType}
+		disabled={!selectedScriptType || blockCount === 0}
 		title={!selectedScriptType ? m.ocr_trigger_btn_disabled() : undefined}
 		onclick={handleClick}
 		class="min-h-[44px] w-full rounded-sm bg-brand-navy font-sans text-sm font-medium text-white transition-colors hover:bg-brand-navy/90 disabled:cursor-not-allowed disabled:opacity-50"
 	>
 		{m.ocr_trigger_btn()}
 	</button>
+	{#if blockCount === 0}
+		<p class="text-xs text-ink-3">{m.ocr_trigger_no_annotations()}</p>
+	{/if}
 </div>