Add custom interval days support for task frequency

- Add customIntervalDays field to Kotlin models (TaskResponse, TaskCreateRequest, TaskUpdateRequest)
- Update Android AddTaskDialog to show interval field only for "Custom" frequency
- Update Android EditTaskScreen for custom frequency support
- Update iOS TaskFormView for custom frequency support
- Fix preview data in TaskCard and TasksSection to include new field
- Add customIntervalDays to OnboardingFirstTaskView

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

composeApp/src/iosMain/kotlin/com/example/casera/storage/TaskCacheManager.ios.kt

@@ -5,6 +5,8 @@ import kotlin.concurrent.Volatile
 
 /**
  * iOS implementation of TaskCacheManager using NSUserDefaults.
+ * Note: iOS widget dirty flag is handled by native Swift WidgetDataManager
+ * using App Groups shared storage, but we provide these methods for KMM compatibility.
  */
 actual class TaskCacheManager {
     private val userDefaults = NSUserDefaults.standardUserDefaults
@@ -23,8 +25,33 @@ actual class TaskCacheManager {
         userDefaults.synchronize()
     }
 
+    /**
+     * Check if tasks need refresh due to widget interactions.
+     * Note: iOS primarily uses native Swift WidgetDataManager for this.
+     */
+    actual fun areTasksDirty(): Boolean {
+        return userDefaults.boolForKey(KEY_DIRTY_FLAG)
+    }
+
+    /**
+     * Mark tasks as dirty (needs refresh).
+     */
+    actual fun markTasksDirty() {
+        userDefaults.setBool(true, KEY_DIRTY_FLAG)
+        userDefaults.synchronize()
+    }
+
+    /**
+     * Clear the dirty flag after tasks have been refreshed.
+     */
+    actual fun clearDirtyFlag() {
+        userDefaults.setBool(false, KEY_DIRTY_FLAG)
+        userDefaults.synchronize()
+    }
+
     companion object {
         private const val KEY_TASKS = "cached_tasks"
+        private const val KEY_DIRTY_FLAG = "tasks_dirty"
 
         @Volatile
         private var instance: TaskCacheManager? = null