feat(translate): add cache_hits counter — backend + frontend

Backend:
- TranslationRun model: add cache_hits Integer column (default 0)
- TranslationRunResponse schema: add cache_hits field
- _helpers.py/_run_list_routes.py/orchestrator_aggregator.py: include
  cache_hits in all run API responses
- _batch_proc.py: count pre_rows served from translation cache per
  batch, return cache_hits in batch result
- executor.py: accumulate cache_hits across batches, persist to run
- Alembic migration: dabc9709 — add cache_hits column to translation_runs

Frontend:
- translationRun.svelte.ts: add cacheHits to store state, WS handler,
  polling handler
- TranslationRunProgress.svelte: 5-col stats grid with purple Cache card
- TranslationRunGlobalIndicator.svelte: 5-col stats with Cache
- TranslationRunResult.svelte: 5-col detail stats with Cache card
- History page: cache_hits shown in run list row + detail panel

Visual: cache hits shown in purple alongside green/yellow/red metrics
(total/success/failed/skipped). Visible during run + in history.

Tests: backend 69/69 translate tests ✅, frontend 698/698 tests ✅,
frontend build ✅

frontend/src/lib/components/translate/TranslationRunGlobalIndicator.svelte

@@ -66,6 +66,7 @@
 	let successfulRecords = $derived(storeState?.successfulRecords || 0);
 	let failedRecords = $derived(storeState?.failedRecords || 0);
 	let skippedRecords = $derived(storeState?.skippedRecords || 0);
+	let cacheHits = $derived(storeState?.cacheHits || 0);
 	let progressPct = $derived(storeState?.progressPct || 0);
 
 	// Auto-dismiss terminal states after a few seconds
@@ -154,7 +155,7 @@
 					</div>
 
 					<!-- Stats grid -->
-					<div class="grid grid-cols-4 gap-2 text-xs">
+					<div class="grid grid-cols-5 gap-2 text-xs">
 						<div class="bg-gray-50 rounded px-2 py-1 text-center">
 							<span class="text-gray-500 block">{($t.translate?.run?.total || 'Total')}</span>
 							<span class="font-bold text-gray-900">{totalRecords}</span>
@@ -171,6 +172,10 @@
 							<span class="text-yellow-600 block">{($t.translate?.run?.skipped || 'Skip')}</span>
 							<span class="font-bold text-yellow-700">{skippedRecords}</span>
 						</div>
+						<div class="bg-purple-50 rounded px-2 py-1 text-center">
+							<span class="text-purple-600 block">Cache</span>
+							<span class="font-bold text-purple-700">{cacheHits}</span>
+						</div>
 					</div>
 				</div>
 			</div>

frontend/src/lib/components/translate/TranslationRunProgress.svelte

@@ -32,6 +32,7 @@
 	let successfulRecords = $derived(storeSnapshot?.successfulRecords || 0);
 	let failedRecords = $derived(storeSnapshot?.failedRecords || 0);
 	let skippedRecords = $derived(storeSnapshot?.skippedRecords || 0);
+	let cacheHits = $derived(storeSnapshot?.cacheHits || 0);
 	let progressPct = $derived(storeSnapshot?.progressPct || 0);
 	let batchCount = $derived(storeSnapshot?.batchCount || 0);
 	let insertStatus = $derived(storeSnapshot?.insertStatus || null);
@@ -96,7 +97,7 @@
 			</div>
 
 			<!-- Statistics -->
-			<div class="grid grid-cols-4 gap-3 text-sm">
+			<div class="grid grid-cols-5 gap-3 text-sm">
 				<div>
 					<span class="text-gray-500">{$t.translate?.run?.total}</span>
 					<p class="font-semibold">{totalRecords}</p>
@@ -113,6 +114,10 @@
 					<span class="text-yellow-600">{$t.translate?.run?.skipped}</span>
 					<p class="font-semibold text-yellow-700">{skippedRecords}</p>
 				</div>
+				<div>
+					<span class="text-purple-600">Cache</span>
+					<p class="font-semibold text-purple-700">{cacheHits}</p>
+				</div>
 			</div>
 
 			<!-- Batch counter -->

frontend/src/lib/components/translate/TranslationRunResult.svelte

@@ -214,7 +214,7 @@
 			</div>
 
 			<!-- Statistics Grid -->
-			<div class="grid grid-cols-2 sm:grid-cols-4 gap-4">
+			<div class="grid grid-cols-2 sm:grid-cols-5 gap-4">
 				<div class="bg-gray-50 rounded-lg p-3">
 					<p class="text-xs text-gray-500 uppercase">{$t.translate?.run?.total_records}</p>
 					<p class="text-xl font-bold text-gray-900">{status.total_records || 0}</p>
@@ -231,6 +231,10 @@
 					<p class="text-xs text-yellow-600 uppercase">{$t.translate?.run?.skipped}</p>
 					<p class="text-xl font-bold text-yellow-700">{status.skipped_records || 0}</p>
 				</div>
+				<div class="bg-purple-50 rounded-lg p-3">
+					<p class="text-xs text-purple-600 uppercase">Cache</p>
+					<p class="text-xl font-bold text-purple-700">{status.cache_hits || 0}</p>
+				</div>
 			</div>
 
 			<!-- Per-language Statistics -->

frontend/src/lib/stores/translationRun.svelte.ts

@@ -27,6 +27,7 @@ export interface TranslationRunState {
 	successfulRecords: number;
 	failedRecords: number;
 	skippedRecords: number;
+	cacheHits: number;
 	progressPct: number;
 	insertStatus: string | null;
 	batchCount: number;
@@ -48,6 +49,7 @@ const initialState: TranslationRunState = {
 	successfulRecords: 0,
 	failedRecords: 0,
 	skippedRecords: 0,
+	cacheHits: 0,
 	progressPct: 0,
 	insertStatus: null,
 	batchCount: 0,
@@ -167,6 +169,7 @@ function _connectWebSocket(runId: string): void {
 						successfulRecords: (data.successful_records as number) || 0,
 						failedRecords: (data.failed_records as number) || 0,
 						skippedRecords: (data.skipped_records as number) || 0,
+						cacheHits: (data.cache_hits as number) || 0,
 						progressPct: pct,
 						insertStatus: insertS || null,
 						batchCount: (data.batch_count as number) || 0,
@@ -268,6 +271,7 @@ async function pollStatus(): Promise<void> {
 			successfulRecords: (data?.successful_records as number) || 0,
 			failedRecords: (data?.failed_records as number) || 0,
 			skippedRecords: (data?.skipped_records as number) || 0,
+			cacheHits: (data?.cache_hits as number) || 0,
 			progressPct: pct,
 			insertStatus: (data?.insert_status as string) || null,
 			batchCount: (data?.batch_count as number) || 0,

frontend/src/routes/translate/history/+page.svelte

@@ -287,6 +287,7 @@
 								<span>{_('translate.history.records_label').replace('{count}', run.total_records || 0)}</span>
 								<span>{_('translate.history.ok_label').replace('{count}', run.successful_records || 0)}</span>
 								<span>{_('translate.history.fail_label').replace('{count}', run.failed_records || 0)}</span>
+								<span class="text-purple-500">Cache: {run.cache_hits || 0}</span>
 								{#if run.created_by}
 									<span>{_('translate.history.by_label').replace('{user}', run.created_by)}</span>
 								{/if}
@@ -407,7 +408,7 @@
 				</div>
 
 				<!-- Stats Grid -->
-				<div class="grid grid-cols-4 gap-3 mb-6">
+				<div class="grid grid-cols-5 gap-3 mb-6">
 					<div class="bg-gray-50 rounded p-3 text-center">
 						<p class="text-lg font-bold text-gray-900">{selectedRunDetail.total_records || 0}</p>
 						<p class="text-xs text-gray-500">{$t.translate?.history?.total}</p>
@@ -424,6 +425,10 @@
 						<p class="text-lg font-bold text-yellow-700">{selectedRunDetail.skipped_records || 0}</p>
 						<p class="text-xs text-yellow-600">{$t.translate?.history?.skipped}</p>
 					</div>
+					<div class="bg-purple-50 rounded p-3 text-center">
+						<p class="text-lg font-bold text-purple-700">{selectedRunDetail.cache_hits || 0}</p>
+						<p class="text-xs text-purple-600">Cache</p>
+					</div>
 				</div>
 
 				<!-- Per-Language Statistics -->