[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/EnumStringTypeHandlerTests.cs

@@ -137,4 +137,107 @@ public class EnumStringTypeHandlerTests
         DapperEnumTypeHandlers.RegisterAll();
         DapperEnumTypeHandlers.RegisterAll();
     }
+
+    [Theory]
+    [InlineData(TileSource.GoogleMaps, "google_maps")]
+    [InlineData(TileSource.Uav, "uav")]
+    public void TileSourceHandler_SetValue_WritesContractWireValue_AZ484(TileSource value, string expected)
+    {
+        // Arrange
+        var handler = new TileSourceTypeHandler();
+        var param = new NpgsqlParameter();
+
+        // Act
+        handler.SetValue(param, value);
+
+        // Assert
+        param.Value.Should().Be(expected);
+        param.DbType.Should().Be(DbType.String);
+    }
+
+    [Theory]
+    [InlineData("google_maps", TileSource.GoogleMaps)]
+    [InlineData("GOOGLE_MAPS", TileSource.GoogleMaps)]
+    [InlineData("uav", TileSource.Uav)]
+    [InlineData("UAV", TileSource.Uav)]
+    public void TileSourceHandler_Parse_AcceptsContractWireValue_AZ484(string raw, TileSource expected)
+    {
+        // Arrange
+        var handler = new TileSourceTypeHandler();
+
+        // Act
+        var result = handler.Parse(raw);
+
+        // Assert
+        result.Should().Be(expected);
+    }
+
+    [Theory]
+    [InlineData(TileSource.GoogleMaps)]
+    [InlineData(TileSource.Uav)]
+    public void TileSourceHandler_RoundTrip_PreservesValue_AZ484(TileSource value)
+    {
+        // Arrange
+        var handler = new TileSourceTypeHandler();
+        var param = new NpgsqlParameter();
+        handler.SetValue(param, value);
+
+        // Act
+        var roundTripped = handler.Parse(param.Value!);
+
+        // Assert
+        roundTripped.Should().Be(value);
+    }
+
+    [Fact]
+    public void TileSourceHandler_Parse_UnknownString_ThrowsDataException_AZ484()
+    {
+        // Arrange
+        var handler = new TileSourceTypeHandler();
+
+        // Act
+        Action act = () => handler.Parse("satar");
+
+        // Assert — Inv-1: unknown sources surface, not silently coerce (coderule.mdc: never suppress errors).
+        act.Should().Throw<DataException>().WithMessage("*satar*");
+    }
+
+    [Fact]
+    public void TileSourceHandler_Parse_NullValue_ThrowsDataException_AZ484()
+    {
+        // Arrange
+        var handler = new TileSourceTypeHandler();
+
+        // Act
+        Action act = () => handler.Parse(null!);
+
+        // Assert
+        act.Should().Throw<DataException>();
+    }
+
+    [Fact]
+    public void TileSourceHandler_Parse_DbNullValue_ThrowsDataException_AZ484()
+    {
+        // Arrange
+        var handler = new TileSourceTypeHandler();
+
+        // Act
+        Action act = () => handler.Parse(DBNull.Value);
+
+        // Assert
+        act.Should().Throw<DataException>();
+    }
+
+    [Fact]
+    public void RegisterAll_RegistersTileSourceHandler_AZ484()
+    {
+        // Arrange / Act
+        DapperEnumTypeHandlers.RegisterAll();
+
+        // Assert — registration is idempotent and the handler emits the contract wire value.
+        var probe = new TileSourceTypeHandler();
+        var param = new NpgsqlParameter();
+        probe.SetValue(param, TileSource.GoogleMaps);
+        param.Value.Should().Be("google_maps");
+    }
 }