[AZ-484] Multi-source tile storage: source + captured_at

Add per-source tile rows to support multi-provider imagery (Google
Maps + future UAV). Migration 013 (transactional) introduces
source/captured_at columns, backfills existing rows to
(source='google_maps', captured_at=created_at), and replaces the
4-column unique index with a 5-column index that includes source.

TileRepository:
- ColumnList includes source + captured_at
- GetByTileCoordinatesAsync returns most-recent row across sources
  (ORDER BY captured_at DESC, updated_at DESC, id DESC)
- GetTilesByRegionAsync uses DISTINCT ON to pick the most-recent
  tile per cell, restoring caller-facing row order
- Insert/Update upsert on the new 5-column conflict key

TileSource enum lives in Common.Enums. Snake_case wire format
(google_maps, uav) is enforced by a focused TileSourceTypeHandler
because the generic ToLowerInvariant pattern would emit
"googlemaps", violating contract v1.0.0.

TileService stamps Source=GoogleMaps + CapturedAt=UtcNow on every
new tile. Tile-storage contract is now frozen at v1.0.0.

AC coverage 7/7. New unit + integration tests cover all ACs;
existing 200 unit + 5 smoke tests preserved.

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

SatelliteProvider.Tests/TileServiceTests.cs

@@ -6,6 +6,7 @@ using Microsoft.Extensions.Options;
 using Moq;
 using SatelliteProvider.Common.Configs;
 using SatelliteProvider.Common.DTO;
+using SatelliteProvider.Common.Enums;
 using SatelliteProvider.Common.Interfaces;
 using SatelliteProvider.DataAccess.Models;
 using SatelliteProvider.DataAccess.Repositories;
@@ -93,6 +94,8 @@ public class TileServiceTests
                 FilePath = "tiles/18/0/0/cached.jpg",
                 TileSizePixels = 256,
                 ImageType = "jpg",
+                Source = TileSource.GoogleMaps,
+                CapturedAt = DateTime.UtcNow,
             },
         };
         tileRepo
@@ -148,6 +151,8 @@ public class TileServiceTests
                 FilePath = "tiles/18/0/0/cached_prior_year.jpg",
                 TileSizePixels = 256,
                 ImageType = "jpg",
+                Source = TileSource.GoogleMaps,
+                CapturedAt = DateTime.UtcNow.AddYears(-1),
             },
         };
         tileRepo
@@ -271,6 +276,8 @@ public class TileServiceTests
             ImageType = "jpg",
             FilePath = "tiles/18/0/0/x.jpg",
             Version = 2026,
+            Source = TileSource.GoogleMaps,
+            CapturedAt = DateTime.UtcNow,
         };
         var tileRepo = new Mock<ITileRepository>();
         tileRepo.Setup(r => r.GetByIdAsync(id)).ReturnsAsync(entity);
@@ -339,7 +346,16 @@ public class TileServiceTests
             var tileRepo = new Mock<ITileRepository>();
             tileRepo
                 .Setup(r => r.GetByTileCoordinatesAsync(z, x, y))
-                .ReturnsAsync(new TileEntity { Id = Guid.NewGuid(), TileZoom = z, TileX = x, TileY = y, FilePath = tempPath });
+                .ReturnsAsync(new TileEntity
+                {
+                    Id = Guid.NewGuid(),
+                    TileZoom = z,
+                    TileX = x,
+                    TileY = y,
+                    FilePath = tempPath,
+                    Source = TileSource.GoogleMaps,
+                    CapturedAt = DateTime.UtcNow,
+                });
 
             var service = BuildService(downloader, tileRepo);
 
@@ -444,6 +460,38 @@ public class TileServiceTests
         capturedToken.Should().Be(cts.Token, "AZ-371 AC-3: caller-supplied CT must reach the downloader");
     }
 
+    [Fact]
+    public void BuildTileEntity_SetsGoogleMapsSourceAndUtcCapturedAt_AZ484_AC5()
+    {
+        // 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);
+        var before = DateTime.UtcNow;
+
+        // Act
+        _ = service.DownloadAndStoreSingleTileAsync(47.46, 37.65, 18).GetAwaiter().GetResult();
+
+        // Assert
+        var after = DateTime.UtcNow;
+        captured.Should().NotBeNull();
+        captured!.Source.Should().Be(TileSource.GoogleMaps,
+            "AZ-484 AC-5: the Google Maps download path stamps Source=GoogleMaps");
+        captured.CapturedAt.Kind.Should().NotBe(DateTimeKind.Local,
+            "captured_at must be UTC per the v1.0.0 storage contract");
+        captured.CapturedAt.Should().BeOnOrAfter(before).And.BeOnOrBefore(after,
+            "AZ-484 AC-5: CapturedAt is the UtcNow at download time");
+    }
+
     [Fact]
     public async Task DownloadAndStoreSingleTileAsync_DownloaderThrows_DoesNotInsert_AZ311_AC2b()
     {