Fix CustomTask model to match API response structure

Updated CustomTask to use nested objects for category, frequency,
priority, and status instead of strings to match the API's actual
response format after recent serializer changes.

Changes:
- category: String → TaskCategory?
- Added frequency: TaskFrequency
- priority: String → TaskPriority
- status: String? → TaskStatus?
- Added next_scheduled_date field
- Added completion_count field

This fixes the JSON parsing error when creating/updating tasks via
the iOS and Android apps, which was caused by the API returning
nested objects like {"id": 21, "name": "Flooring"} but the model
expecting simple strings.

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

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

composeApp/src/commonMain/kotlin/com/example/mycrib/models/CustomTask.kt

@@ -11,12 +11,15 @@ data class CustomTask (
     @SerialName("created_by_username") val createdByUsername: String,
     val title: String,
     val description: String? = null,
-    val category: String,
+    val category: TaskCategory?,
-    val priority: String,
+    val frequency: TaskFrequency,
-    val status: String? = null,
+    val priority: TaskPriority,
+    val status: TaskStatus? = null,
     @SerialName("due_date") val dueDate: String?,
+    @SerialName("next_scheduled_date") val nextScheduledDate: String? = null,
     @SerialName("estimated_cost") val estimatedCost: String? = null,
     @SerialName("actual_cost") val actualCost: String? = null,
+    @SerialName("completion_count") val completionCount: Int? = null,
     val notes: String? = null,
     val archived: Boolean = false,
     @SerialName("created_at") val createdAt: String,