[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.DataAccess/Models/TileEntity.cs

@@ -16,7 +16,11 @@ public class TileEntity
     public string? MapsVersion { get; set; }
     public int? Version { get; set; }
     public string FilePath { get; set; } = string.Empty;
-    public TileSource Source { get; set; }
+    // AZ-484: stored as the contract wire value (snake_case string). See
+    // TileSourceConverter for enum<->wire conversion. Cannot use the
+    // TileSource enum directly because Dapper bypasses TypeHandler<T> for
+    // enum types during read deserialization (Dapper issue #259).
+    public string Source { get; set; } = TileSourceConverter.GoogleMapsWireValue;
     public DateTime CapturedAt { get; set; }
     public DateTime CreatedAt { get; set; }
     public DateTime UpdatedAt { get; set; }