feat(risk-control): record matched keyword in keyword-block logs

The risk control center's moderation log records had no field for the
keyword that triggered a keyword block, so the admin UI couldn't show
which keyword was hit (only the application slog logged it).

- migration 156: add matched_keyword column to content_moderation_logs
- ContentModerationLog gains MatchedKeyword; set it on keyword block
- repo CreateLog/ListLogs persist and read the column
- frontend: show "命中关键词" inline in the log table and detail modal
- i18n: add matchedKeyword (zh/en)

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

frontend/src/views/admin/RiskControlView.vue

@@ -317,6 +317,9 @@
                     <td class="whitespace-nowrap px-5 py-4 text-sm text-gray-700 dark:text-gray-300">
                       <div>{{ row.highest_category || '-' }}</div>
                       <div class="text-xs text-gray-400">{{ percent(row.highest_score) }}</div>
+                      <div v-if="row.matched_keyword" class="mt-0.5 text-xs font-medium text-red-600 dark:text-red-300" :title="t('admin.riskControl.matchedKeyword') + ': ' + row.matched_keyword">
+                        {{ t('admin.riskControl.matchedKeyword') }}: {{ row.matched_keyword }}
+                      </div>
                     </td>
                     <td class="whitespace-nowrap px-5 py-4 text-sm text-gray-700 dark:text-gray-300">
                       <div>{{ violationCountText(row) }}</div>
@@ -1078,6 +1081,10 @@
                 {{ inputDetailRow.highest_category || '-' }} / {{ percent(inputDetailRow.highest_score) }}
               </p>
             </div>
+            <div v-if="inputDetailRow.matched_keyword" class="rounded-lg border border-red-100 bg-red-50 p-4 dark:border-red-900/60 dark:bg-red-900/20">
+              <p class="text-xs font-medium text-red-500 dark:text-red-300">{{ t('admin.riskControl.matchedKeyword') }}</p>
+              <p class="mt-1 truncate text-sm font-semibold text-red-700 dark:text-red-200" :title="inputDetailRow.matched_keyword">{{ inputDetailRow.matched_keyword }}</p>
+            </div>
           </div>
 
           <div class="rounded-xl border border-gray-100 bg-white p-4 shadow-sm dark:border-dark-700 dark:bg-dark-800">