[AZ-484] Fix multi-source tile reads: drop Dapper enum handler

Two integration-test failures uncovered after the initial commit:

1) GetTilesByRegionAsync outer ORDER BY referenced 'updated_at' but
   the inner DISTINCT ON subquery aliased it to 'UpdatedAt' (Postgres
   folds to 'updatedat'). DISTINCT ON already guarantees one row per
   (latitude, longitude, ...) so the third tiebreak was unreachable;
   removed it.

2) Dapper 2.1.35 silently bypasses SqlMapper.TypeHandler<T> for enum
   types during read deserialization (Dapper issue #259). The
   TileSourceTypeHandler worked for writes but reads fell through to
   Enum.TryParse, which cannot map 'google_maps' to GoogleMaps.

   Pivoted: TileEntity.Source is now a string (the wire value).
   TileSource enum stays as the public producer surface in
   Common.Enums; TileSourceConverter (Common.Enums) provides
   ToWireValue / FromWireValue / IsValidWireValue at the boundary.
   TileSourceTypeHandler deleted; registration removed from
   DapperEnumTypeHandlers.RegisterAll.

   tile-storage.md Inv-5 amended to document the storage choice.
   _docs/LESSONS.md L-001 records the Dapper bypass for future cycles.

Full suite passes (213 unit + integration suite incl. AZ-484
AC-1..AC-5, security SEC-01..SEC-04, AZ-356/362/357).

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

SatelliteProvider.Tests/TileServiceTests.cs

@@ -94,7 +94,7 @@ public class TileServiceTests
                 FilePath = "tiles/18/0/0/cached.jpg",
                 TileSizePixels = 256,
                 ImageType = "jpg",
-                Source = TileSource.GoogleMaps,
+                Source = TileSourceConverter.ToWireValue(TileSource.GoogleMaps),
                 CapturedAt = DateTime.UtcNow,
             },
         };
@@ -151,7 +151,7 @@ public class TileServiceTests
                 FilePath = "tiles/18/0/0/cached_prior_year.jpg",
                 TileSizePixels = 256,
                 ImageType = "jpg",
-                Source = TileSource.GoogleMaps,
+                Source = TileSourceConverter.ToWireValue(TileSource.GoogleMaps),
                 CapturedAt = DateTime.UtcNow.AddYears(-1),
             },
         };
@@ -276,7 +276,7 @@ public class TileServiceTests
             ImageType = "jpg",
             FilePath = "tiles/18/0/0/x.jpg",
             Version = 2026,
-            Source = TileSource.GoogleMaps,
+            Source = TileSourceConverter.ToWireValue(TileSource.GoogleMaps),
             CapturedAt = DateTime.UtcNow,
         };
         var tileRepo = new Mock<ITileRepository>();
@@ -353,7 +353,7 @@ public class TileServiceTests
                     TileX = x,
                     TileY = y,
                     FilePath = tempPath,
-                    Source = TileSource.GoogleMaps,
+                    Source = TileSourceConverter.ToWireValue(TileSource.GoogleMaps),
                     CapturedAt = DateTime.UtcNow,
                 });
 
@@ -484,8 +484,8 @@ public class TileServiceTests
         // 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!.Source.Should().Be(TileSourceConverter.ToWireValue(TileSource.GoogleMaps),
+            "AZ-484 AC-5: the Google Maps download path stamps Source='google_maps' (contract wire value)");
         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,