Fix 7 data mutation layer risks identified in audit

- save()/saveAndRunDataListeners() now return @discardableResult Bool;
  listeners only fire on successful save
- MoodLogger.updateMood() now recalculates streak, updates Live Activity,
  and notifies watch (was missing these side effects)
- CSV import uses new addBatch()/importMoods() for O(1) side effects
  instead of O(n) per-row widget reloads and streak calcs
- Foreground task ordering: fillInMissingDates() now runs before
  removeDuplicates() so backfill-created duplicates are caught same cycle
- WidgetMoodSaver deletes ALL entries for date (was fetchLimit=1, leaving
  CloudKit sync duplicates behind)
- cleanupPhotoIfNeeded logs warning on failed photo deletion instead of
  silently orphaning files

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Shared/Persisence/DataControllerProtocol.swift

@@ -70,10 +70,12 @@ protocol MoodDataDeleting {
 @MainActor
 protocol MoodDataPersisting {
     /// Save pending changes
-    func save()
+    @discardableResult
+    func save() -> Bool
 
     /// Save and notify listeners
-    func saveAndRunDataListeners()
+    @discardableResult
+    func saveAndRunDataListeners() -> Bool
 
     /// Add a listener for data changes
     func addNewDataListener(closure: @escaping (() -> Void))