[AZ-373] Refactor C20: drop MapsVersion from new writes (option a)

- Stop writing "downloaded_YYYY-MM-DD" into tiles.maps_version: new rows
  bind @MapsVersion to NULL via TileService.BuildTileEntity.
- Retain the tiles.maps_version column (coderule.mdc forbids unprompted
  column drops); pre-existing rows keep their values for forensics.
- Remove MapsVersion property from DownloadTileResponse (API wire shape)
  and TileMetadata (internal DTO); OpenAPI schema regenerates from the
  DTO via Swashbuckle.
- Add 3 AC tests in TileServiceTests covering the captured-entity write
  (AC-1) and the DTO/wire-shape removal (AC-2).
- Update integration-test local DTO + console output; refresh docs in
  common_dtos.md, services_tile_service.md, data_model.md.
- Archive AZ-373 task file: todo/ -> done/.

174 unit + 5 smoke pass.

Co-authored-by: Cursor <cursoragent@cursor.com>

SatelliteProvider.Tests/TileServiceTests.cs

@@ -207,6 +207,54 @@ public class TileServiceTests
         captured!.Version.Should().BeNull("AZ-357: new code never writes the deprecated year-based version");
     }
 
+    [Fact]
+    public void BuildTileEntity_DoesNotPopulateMapsVersion_AZ373_AC1()
+    {
+        // Arrange
+        var downloader = new Mock<ISatelliteDownloader>();
+        var tileRepo = new Mock<ITileRepository>();
+        TileEntity? captured = null;
+        tileRepo
+            .Setup(r => r.InsertAsync(It.IsAny<TileEntity>()))
+            .Callback<TileEntity>(e => captured = e)
+            .ReturnsAsync(Guid.NewGuid());
+        downloader
+            .Setup(d => d.DownloadSingleTileAsync(It.IsAny<double>(), It.IsAny<double>(), It.IsAny<int>(), It.IsAny<CancellationToken>()))
+            .ReturnsAsync(new DownloadedTileInfoV2(1, 2, 18, 47.46, 37.65, "tiles/18/1/2.jpg", 100.0));
+
+        var service = BuildService(downloader, tileRepo);
+
+        // Act
+        _ = service.DownloadAndStoreSingleTileAsync(47.46, 37.65, 18).GetAwaiter().GetResult();
+
+        // Assert
+        captured.Should().NotBeNull();
+        captured!.MapsVersion.Should().BeNull(
+            "AZ-373 option (a): new code never writes a MapsVersion value; the column is retained for forensics on pre-existing rows only");
+    }
+
+    [Fact]
+    public void DownloadTileResponse_DoesNotExposeMapsVersion_AZ373_AC2()
+    {
+        // Act
+        var property = typeof(DownloadTileResponse).GetProperty("MapsVersion");
+
+        // Assert
+        property.Should().BeNull(
+            "AZ-373 AC-2 option (a): MapsVersion is removed from the HTTP response shape");
+    }
+
+    [Fact]
+    public void TileMetadata_DoesNotExposeMapsVersion_AZ373_AC1()
+    {
+        // Act
+        var property = typeof(TileMetadata).GetProperty("MapsVersion");
+
+        // Assert
+        property.Should().BeNull(
+            "AZ-373 AC-1: TileMetadata DTO no longer carries MapsVersion (consistent with the HTTP response removal)");
+    }
+
     [Fact]
     public async Task GetTileAsync_KnownId_ReturnsMappedMetadata()
     {