fix(inventory): merge draft + list watch into one subscription

InventoryCubit subscribed to watchInventory() and watchDrafts()
separately — two overlapping StreamGroups (both watching attachments)
re-emitted in a tight loop that starved the event loop and hung widget
tests' pumpAndSettle for 10+ minutes (home/inventory/quick-add all
timed out). Replace both with a single watchInventoryView() stream that
loads the catalogued list and the draft tray from one StreamGroup.

Full widget suite no longer hangs: 165 pass. One unrelated failure
remains in the v8 variety edit sheet (Save button pushed off-screen by
new fields).

apps/app_seeds/lib/data/variety_repository.dart

@@ -365,6 +365,27 @@ class VarietyRepository {
     return triggers.asyncMap((_) => _loadInventory());
   }
 
+  /// The whole inventory screen in one reactive subscription: the catalogued
+  /// list and the draft tray, from a single [StreamGroup]. The cubit MUST use
+  /// this rather than subscribing to [watchInventory] and [watchDrafts]
+  /// separately — two overlapping StreamGroups (both watching `attachments`)
+  /// re-emit in a tight loop that starves the event loop and hangs widget
+  /// tests' `pumpAndSettle`.
+  Stream<({List<VarietyListItem> items, List<VarietyListItem> drafts})>
+  watchInventoryView() {
+    final triggers = StreamGroup.merge<void>([
+      (_db.select(
+        _db.varieties,
+      )..where((v) => v.isDeleted.equals(false))).watch().map((_) {}),
+      _db.select(_db.attachments).watch().map((_) {}),
+      _db.select(_db.species).watch().map((_) {}),
+      _db.select(_db.lots).watch().map((_) {}),
+    ]);
+    return triggers.asyncMap(
+      (_) async => (items: await _loadInventory(), drafts: await _loadDrafts()),
+    );
+  }
+
   Future<List<VarietyListItem>> _loadInventory() async {
     final rows =
         await (_db.select(_db.varieties)