[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.Services.TileDownloader/TileService.cs

@@ -154,7 +154,7 @@ public class TileService : ITileService
             TileSizeMeters = downloaded.TileSizeMeters,
             TileSizePixels = _mapConfig.TileSizePixels,
             ImageType = "jpg",
-            MapsVersion = $"downloaded_{now:yyyy-MM-dd}",
+            MapsVersion = null,
             Version = null,
             FilePath = downloaded.FilePath,
             CreatedAt = now,
@@ -175,7 +175,6 @@ public class TileService : ITileService
             TileSizeMeters = entity.TileSizeMeters,
             TileSizePixels = entity.TileSizePixels,
             ImageType = entity.ImageType,
-            MapsVersion = entity.MapsVersion,
             Version = entity.Version,
             FilePath = entity.FilePath,
             CreatedAt = entity.CreatedAt,