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.Data/Configurations/ImportBatchConfiguration.cs

@@ -12,6 +12,7 @@ public class ImportBatchConfiguration : IEntityTypeConfiguration<ImportBatch>
         builder.HasKey(b => b.Id);
         builder.Property(b => b.FileName).HasMaxLength(500).IsRequired();
         builder.Property(b => b.FileType).HasMaxLength(50).IsRequired();
+        builder.Property(b => b.ParsedDataJson).HasColumnType("text");
 
         builder.HasOne(b => b.User)
             .WithMany()

src/Purrse.Data/Migrations/20260208155836_AddParsedDataToImportBatch.cs

@@ -0,0 +1,28 @@
+using Microsoft.EntityFrameworkCore.Migrations;
+
+#nullable disable
+
+namespace Purrse.Data.Migrations
+{
+    /// <inheritdoc />
+    public partial class AddParsedDataToImportBatch : Migration
+    {
+        /// <inheritdoc />
+        protected override void Up(MigrationBuilder migrationBuilder)
+        {
+            migrationBuilder.AddColumn<string>(
+                name: "ParsedDataJson",
+                table: "import_batches",
+                type: "text",
+                nullable: true);
+        }
+
+        /// <inheritdoc />
+        protected override void Down(MigrationBuilder migrationBuilder)
+        {
+            migrationBuilder.DropColumn(
+                name: "ParsedDataJson",
+                table: "import_batches");
+        }
+    }
+}

src/Purrse.Data/Migrations/PurrseDbContextModelSnapshot.cs

@@ -249,6 +249,9 @@ namespace Purrse.Data.Migrations
                     b.Property<int>("ImportedCount")
                         .HasColumnType("integer");
 
+                    b.Property<string>("ParsedDataJson")
+                        .HasColumnType("text");
+
                     b.Property<int>("SkippedCount")
                         .HasColumnType("integer");