Implement Phase 2: end-to-end import system

Complete the import flow from file upload through duplicate resolution
to transaction creation. Previously, ResolveDuplicatesAsync was a stub
that only incremented counters, FileWatcherService detected files but
didn't process them, and ImportsView.vue ignored the API response.

Backend:
- Add ParsedDataJson column to ImportBatch to persist parsed data
  between upload and confirm steps
- Rewrite ImportService.ResolveDuplicatesAsync to deserialize parsed
  transactions and create/merge/skip based on user decisions, with
  payee matching, fingerprinting, and account balance updates
- Add GetBatchesAsync for import history
- Complete FileWatcherService: wait for file ready, resolve account by
  filename, call UploadAsync, send SignalR notification, archive file
- Add GET /api/imports/batches endpoint

Frontend:
- Create imports API service (frontend/src/services/imports.ts)
- Add ImportBatch, DuplicateResolution types
- Rewrite ImportsView.vue with 3-step Vuetify stepper wizard:
  upload, review with duplicate handling, completion summary,
  plus import history table

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

frontend/src/services/imports.ts

@@ -0,0 +1,21 @@
+import api from './api'
+import type { ImportUploadResponse, ImportBatch, ResolveDuplicatesRequest } from '@/types'
+
+export const importsApi = {
+  upload: (accountId: string, file: File) => {
+    const formData = new FormData()
+    formData.append('file', file)
+    return api.post<ImportUploadResponse>(`/imports/upload?accountId=${accountId}`, formData, {
+      headers: { 'Content-Type': 'multipart/form-data' }
+    })
+  },
+
+  confirmBatch: (batchId: string) =>
+    api.post<ImportBatch>(`/imports/batches/${batchId}/confirm`),
+
+  resolveDuplicates: (batchId: string, request: ResolveDuplicatesRequest) =>
+    api.post<ImportBatch>(`/imports/batches/${batchId}/resolve-duplicates`, request),
+
+  getBatches: () =>
+    api.get<ImportBatch[]>('/imports/batches'),
+}