[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/Repositories/TileRepository.cs

@@ -70,7 +70,9 @@ public class TileRepository : ITileRepository
         // AZ-484 selection rule: at most one row per (lat, lon, zoom, size) cell, picking
         // the most-recent across sources via DISTINCT ON, with deterministic tie-break on
         // (captured_at DESC, updated_at DESC, id DESC). The outer ORDER BY restores the
-        // pre-AZ-484 caller-facing order (latitude DESC, longitude ASC, updated_at DESC).
+        // pre-AZ-484 caller-facing order (latitude DESC, longitude ASC); the pre-AZ-484
+        // updated_at DESC tiebreak is unreachable here because DISTINCT ON already
+        // guarantees one row per (latitude, longitude, ...) tuple.
         const string sql = $@"
             SELECT * FROM (
                 SELECT DISTINCT ON (latitude, longitude, tile_zoom, tile_size_meters)
@@ -82,7 +84,7 @@ public class TileRepository : ITileRepository
                 ORDER BY latitude, longitude, tile_zoom, tile_size_meters,
                          captured_at DESC, updated_at DESC, id DESC
             ) deduped
-            ORDER BY latitude DESC, longitude ASC, updated_at DESC";
+            ORDER BY latitude DESC, longitude ASC";
 
         var stopwatch = Stopwatch.StartNew();
         var tiles = await connection.QueryAsync<TileEntity>(sql, new