fix(sites): preserve original timestamps in site merge undo

SiteSpeciesSnapshot was missing createdAt, and undoMerge was
overwriting both site and species timestamps with the current time.
Add createdAt to SiteSpeciesSnapshot, capture raw DB timestamps for
deleted sites in MergeSnapshot, and restore originals on undo.

Mirrors the same fixes applied to buddy merge in PR #66.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: ericgriffin

lib/features/dive_sites/data/repositories/site_repository_impl.dart

@@ -240,6 +240,15 @@ class SiteRepository {
           if (media.siteId != null) media.id: media.siteId!,
       };
 
+      // Capture raw timestamps for deleted sites (domain entity lacks these)
+      final rawSiteRows = await (_db.select(
+        _db.diveSites,
+      )..where((t) => t.id.isIn(orderedIds))).get();
+      final siteTimestamps = {
+        for (final row in rawSiteRows)
+          row.id: (createdAt: row.createdAt, updatedAt: row.updatedAt),
+      };
+
       final allSpeciesRows = await (_db.select(
         _db.siteSpecies,
       )..where((t) => t.siteId.isIn(orderedIds))).get();
@@ -250,6 +259,7 @@ class SiteRepository {
               siteId: row.siteId,
               speciesId: row.speciesId,
               notes: row.notes,
+              createdAt: row.createdAt,
             ),
           )
           .toList(growable: false);
@@ -309,6 +319,11 @@ class SiteRepository {
         mediaOriginalSiteIds: mediaOriginalSiteIds,
         deletedSpeciesEntries: deletedSpecies,
         modifiedSpeciesEntries: modifiedSpecies,
+        deletedSiteTimestamps: {
+          for (final id in duplicateIds)
+            if (siteTimestamps.containsKey(id)) id: siteTimestamps[id]!,
+        },
+        survivorTimestamps: siteTimestamps[survivorId],
       );
     } catch (e, stackTrace) {
       _log.error('Failed to merge sites: $siteIds', e, stackTrace);
@@ -340,6 +355,7 @@ class SiteRepository {
 
         // 2. Re-create deleted sites
         for (final site in snapshot.deletedSites) {
+          final ts = snapshot.deletedSiteTimestamps[site.id];
           await _db
               .into(_db.diveSites)
               .insert(
@@ -362,8 +378,8 @@ class SiteRepository {
                   mooringNumber: Value(site.mooringNumber),
                   parkingInfo: Value(site.parkingInfo),
                   altitude: Value(site.altitude),
-                  createdAt: Value(now),
-                  updatedAt: Value(now),
+                  createdAt: Value(ts?.createdAt ?? now),
+                  updatedAt: Value(ts?.updatedAt ?? now),
                 ),
               );
           await _syncRepository.markRecordPending(
@@ -411,7 +427,7 @@ class SiteRepository {
                   siteId: Value(entry.siteId),
                   speciesId: Value(entry.speciesId),
                   notes: Value(entry.notes),
-                  createdAt: Value(now),
+                  createdAt: Value(entry.createdAt),
                 ),
               );
           await _syncRepository.markRecordPending(
@@ -714,13 +730,23 @@ class MergeSnapshot {
   final List<SiteSpeciesSnapshot> deletedSpeciesEntries;
   final List<SiteSpeciesSnapshot> modifiedSpeciesEntries;
 
+  /// Original createdAt/updatedAt for each deleted site, keyed by site ID.
+  /// DiveSite domain entity does not carry timestamps, so they are captured
+  /// separately from the database row before deletion.
+  final Map<String, ({int createdAt, int updatedAt})> deletedSiteTimestamps;
+
+  /// Original createdAt/updatedAt for the survivor site before merge.
+  final ({int createdAt, int updatedAt})? survivorTimestamps;
+
   const MergeSnapshot({
     required this.originalSurvivor,
     required this.deletedSites,
     required this.diveOriginalSiteIds,
     required this.mediaOriginalSiteIds,
     required this.deletedSpeciesEntries,
     required this.modifiedSpeciesEntries,
+    this.deletedSiteTimestamps = const {},
+    this.survivorTimestamps,
   });
 }
 
@@ -730,11 +756,13 @@ class SiteSpeciesSnapshot {
   final String siteId;
   final String speciesId;
   final String notes;
+  final int createdAt;
 
   const SiteSpeciesSnapshot({
     required this.id,
     required this.siteId,
     required this.speciesId,
     required this.notes,
+    required this.createdAt,
   });
 }