[AZ-357] Refactor C06: drop tile Version concept; cumulative review batches 7-9

AZ-357 — eliminate year-based tile cache expiry (LF-1):
- Migration 012: drop 5-col unique index, dedupe by (lat,lon,zoom,
  size) keeping max(updated_at), add new 4-col unique index, make
  version column nullable + drop default. Column itself preserved
  per coderule (column drops require explicit confirmation; tracked
  in AZ-373 / C20).
- TileEntity.Version, TileMetadata.Version, DownloadTileResponse.
  Version: int -> int? (HTTP shape preserved; field still in JSON).
- TileService.DownloadAndStoreTilesAsync: drop currentVersion year
  computation and the .Where(t => t.Version == currentVersion)
  cache filter. BuildTileEntity: drop year arg; write Version=null.
- TileRepository: ON CONFLICT now 4-col; lookup queries
  ORDER BY updated_at DESC instead of version DESC.
- Tests: replace inverted BT02b with positive AZ357_AC1
  (prior-year cached tile is reused). Add BuildTileEntity_
  DoesNotPopulateVersion_AZ357 to enforce the no-write contract.
- 69 unit + 5 smoke + 3 stub-contract integration tests pass.

Cumulative code review (batches 7-9, 7 tasks): VERDICT=PASS.
Report at _docs/03_implementation/reviews/batch_09_review.md.
Zero Critical/High/Medium/Low findings. Architecture baseline
remains clean.

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

SatelliteProvider.Tests/TileServiceTests.cs

@@ -128,13 +128,13 @@ public class TileServiceTests
     }
 
     [Fact]
-    public async Task DownloadAndStoreTilesAsync_IgnoresStaleVersionCachedTiles_BT02b()
+    public async Task DownloadAndStoreTilesAsync_TreatsCachedTileFromPriorYearAsFresh_AZ357_AC1()
     {
         // Arrange
         var downloader = new Mock<ISatelliteDownloader>();
         var tileRepo = new Mock<ITileRepository>();
 
-        var stale = new List<TileEntity>
+        var priorYearCached = new List<TileEntity>
         {
             new()
             {
@@ -143,13 +143,15 @@ public class TileServiceTests
                 Latitude = TestCoordinates.TileLat,
                 Longitude = TestCoordinates.TileLon,
                 Version = DateTime.UtcNow.Year - 1,
-                FilePath = "tiles/18/0/0/old.jpg",
+                FilePath = "tiles/18/0/0/cached_prior_year.jpg",
+                TileSizePixels = 256,
+                ImageType = "jpg",
             },
         };
         tileRepo
             .Setup(r => r.GetTilesByRegionAsync(
                 It.IsAny<double>(), It.IsAny<double>(), It.IsAny<double>(), It.IsAny<int>()))
-            .ReturnsAsync(stale);
+            .ReturnsAsync(priorYearCached);
 
         IEnumerable<ExistingTileInfo>? capturedExisting = null;
         downloader
@@ -161,10 +163,7 @@ public class TileServiceTests
                 It.IsAny<CancellationToken>()))
             .Callback<GeoPoint, double, int, IEnumerable<ExistingTileInfo>, CancellationToken>(
                 (_, _, _, e, _) => capturedExisting = e.ToList())
-            .ReturnsAsync(new List<DownloadedTileInfoV2>
-            {
-                MakeDownloaded(123, 456, TestCoordinates.DefaultZoom, TestCoordinates.TileLat, TestCoordinates.TileLon),
-            });
+            .ReturnsAsync(new List<DownloadedTileInfoV2>());
 
         var service = BuildService(downloader, tileRepo);
 
@@ -173,10 +172,38 @@ public class TileServiceTests
             TestCoordinates.TileLat, TestCoordinates.TileLon, 200, TestCoordinates.DefaultZoom);
 
         // Assert
-        capturedExisting.Should().BeEmpty(
-            "stale-version tiles must not be passed to the downloader as 'already have it'");
-        result.Should().HaveCount(1, "only the freshly-downloaded tile is in the result");
-        tileRepo.Verify(r => r.InsertAsync(It.IsAny<TileEntity>()), Times.Once);
+        capturedExisting.Should().NotBeNull();
+        capturedExisting!.Should().ContainSingle(
+            "after AZ-357 the version column no longer gates the cache; the prior-year row is reusable");
+        result.Should().HaveCount(1);
+        result[0].Id.Should().Be(priorYearCached[0].Id);
+        tileRepo.Verify(r => r.InsertAsync(It.IsAny<TileEntity>()), Times.Never,
+            "cached tile from prior year must not be re-inserted");
+    }
+
+    [Fact]
+    public void BuildTileEntity_DoesNotPopulateVersion_AZ357()
+    {
+        // 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!.Version.Should().BeNull("AZ-357: new code never writes the deprecated year-based version");
     }
 
     [Fact]