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>

src/Purrse.Api/Controllers/ImportsController.cs

@@ -32,9 +32,13 @@ public class ImportsController : ControllerBase
         => Ok(await _importService.ConfirmBatchAsync(UserId, batchId));
 
     [HttpPost("batches/{batchId}/resolve-duplicates")]
-    public async Task<ActionResult> ResolveDuplicates(Guid batchId, ResolveDuplicatesRequest request)
+    public async Task<ActionResult<ImportBatchResponse>> ResolveDuplicates(Guid batchId, ResolveDuplicatesRequest request)
     {
-        await _importService.ResolveDuplicatesAsync(UserId, batchId, request);
-        return NoContent();
+        var result = await _importService.ResolveDuplicatesAsync(UserId, batchId, request);
+        return Ok(result);
     }
+
+    [HttpGet("batches")]
+    public async Task<ActionResult<List<ImportBatchResponse>>> GetBatches()
+        => Ok(await _importService.GetBatchesAsync(UserId));
 }