feat: force a seller scan over active conversations from the inbox

Adds a "Scan for sellers" button to the conversations header, backed by
POST /api/conversations/seller-scan.

The sweep reuses the existing seller detection rather than inventing a
second one: the configured keyword/domain list, the seller-link funnel
patterns, and the aiReplyScreening confidences all decide the verdict, so
a swept conversation lands in the state the live reply loop would have
given it. Being operator-forced, it deliberately ignores filterSellers
and aiReplyScreening.enabled.

AI is the last resort. Conversations are skipped when already flagged or
killed, settled for free by the deterministic rules, or skipped against a
durable sellerScreenedKey watermark when nothing new has arrived since
the last clean sweep. Only the remainder reaches the model, batched eight
at a time through a new screenConversationsForSellers, so the system
prompt and round trip are paid per batch instead of per conversation. A
classifier outage degrades the sweep instead of failing it.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

apps/dashboard/src/features/conversations/conversation-api.ts

@@ -13,6 +13,7 @@ import {
   SuggestedReplyResponseSchema,
   BulkMarkConversationsReadRequestSchema,
   BulkMarkConversationsReadResponseSchema,
+  SellerScanResponseSchema,
   MarkConversationReadRequestSchema,
   MarkConversationUnreadRequestSchema,
   SetConversationStatusRequestSchema,
@@ -22,6 +23,7 @@ import {
   type ConversationMediaShareOptions,
   type ConversationTriageStatus,
   type ProcessedPost,
+  type SellerScanResponse,
   type SuccessResponse,
 } from '../../../../../packages/api-contracts/src/index.js';
 import { createDashboardRequest } from '../../api/request.js';
@@ -53,6 +55,7 @@ export interface ConversationApi {
   markUnread(id: string, beforeTimestamp?: number): Promise<SuccessResponse>;
   setStatus(id: string, status: ConversationTriageStatus, snoozeUntil?: number | null): Promise<SuccessResponse>;
   bulkMarkRead(ids: string[]): Promise<BulkMarkConversationsReadResponse>;
+  sellerScan(): Promise<SellerScanResponse>;
 }
 
 function jsonPost(body: unknown): RequestInit {
@@ -174,6 +177,12 @@ export function createConversationApi(fetchImplementation?: typeof fetch): Conve
         BulkMarkConversationsReadResponseSchema,
       );
     },
+    async sellerScan() {
+      return parseResponse(
+        await request('/api/conversations/seller-scan', { method: 'POST' }),
+        SellerScanResponseSchema,
+      );
+    },
   };
 }