[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.Services.TileDownloader/TileService.cs

@@ -33,40 +33,38 @@ public class TileService : ITileService
     }
 
     public async Task<List<TileMetadata>> DownloadAndStoreTilesAsync(
-        double latitude, 
-        double longitude, 
-        double sizeMeters, 
-        int zoomLevel, 
+        double latitude,
+        double longitude,
+        double sizeMeters,
+        int zoomLevel,
         CancellationToken cancellationToken = default)
     {
-        var currentVersion = DateTime.UtcNow.Year;
-        
         var existingTiles = await _tileRepository.GetTilesByRegionAsync(latitude, longitude, sizeMeters, zoomLevel);
-        var existingTilesList = existingTiles.Where(t => t.Version == currentVersion).ToList();
-        
+        var existingTilesList = existingTiles.ToList();
+
         var centerPoint = new GeoPoint(latitude, longitude);
-        
+
         var existingTileInfos = existingTilesList
             .Select(t => new ExistingTileInfo(t.Latitude, t.Longitude, t.TileZoom))
             .ToList();
-        
+
         var downloadedTiles = await _downloader.GetTilesWithMetadataAsync(
-            centerPoint, 
-            sizeMeters / 2, 
-            zoomLevel, 
+            centerPoint,
+            sizeMeters / 2,
+            zoomLevel,
             existingTileInfos,
             cancellationToken);
-        
+
         var result = new List<TileMetadata>();
-        
+
         foreach (var existingTile in existingTilesList)
         {
             result.Add(MapToMetadata(existingTile));
         }
-        
+
         foreach (var downloadedTile in downloadedTiles)
         {
-            var tileEntity = BuildTileEntity(downloadedTile, currentVersion);
+            var tileEntity = BuildTileEntity(downloadedTile);
             await _tileRepository.InsertAsync(tileEntity);
             result.Add(MapToMetadata(tileEntity));
         }
@@ -110,7 +108,7 @@ public class TileService : ITileService
         {
             var tileCenter = GeoUtils.TileToWorldPos(x, y, z);
             var downloaded = await _downloader.DownloadSingleTileAsync(tileCenter.Lat, tileCenter.Lon, z, cancellationToken);
-            var entity = BuildTileEntity(downloaded, DateTime.UtcNow.Year);
+            var entity = BuildTileEntity(downloaded);
             await _tileRepository.InsertAsync(entity);
             filePath = entity.FilePath;
         }
@@ -132,12 +130,12 @@ public class TileService : ITileService
         CancellationToken cancellationToken = default)
     {
         var downloaded = await _downloader.DownloadSingleTileAsync(latitude, longitude, zoomLevel, cancellationToken);
-        var entity = BuildTileEntity(downloaded, DateTime.UtcNow.Year);
+        var entity = BuildTileEntity(downloaded);
         await _tileRepository.InsertAsync(entity);
         return MapToMetadata(entity);
     }
 
-    private static TileEntity BuildTileEntity(DownloadedTileInfoV2 downloaded, int currentVersion)
+    private static TileEntity BuildTileEntity(DownloadedTileInfoV2 downloaded)
     {
         var now = DateTime.UtcNow;
         return new TileEntity
@@ -152,7 +150,7 @@ public class TileService : ITileService
             TileSizePixels = 256,
             ImageType = "jpg",
             MapsVersion = $"downloaded_{now:yyyy-MM-dd}",
-            Version = currentVersion,
+            Version = null,
             FilePath = downloaded.FilePath,
             CreatedAt = now,
             UpdatedAt = now