Add Re-sync button for SimpleFIN connections

Resets LastSyncAt on all linked accounts so the next sync
re-fetches the full 90-day transaction window. Duplicate
detection prevents re-importing existing transactions.

- POST /api/bank-sync/connections/{id}/reset-sync endpoint
- Re-sync button shown only on SimpleFIN connection cards

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

frontend/src/services/bankSync.ts

@@ -46,6 +46,9 @@ export const bankSyncApi = {
   updateLinkedAccount: (linkedAccountId: string, data: { accountId: string | null; isEnabled: boolean }) =>
     api.put<LinkedAccountInfo>(`/bank-sync/linked-accounts/${linkedAccountId}`, data),
 
+  resetSync: (connectionId: string) =>
+    api.post(`/bank-sync/connections/${connectionId}/reset-sync`),
+
   syncNow: (connectionId: string) =>
     api.post(`/bank-sync/connections/${connectionId}/sync-now`),