[BUG] [Tasks] Task improvements

Tasks – Subtasks
: Fixed issue where completed parent tasks reverted to "To Do" after refresh and resolved missing subtask duplication.
Tasks – Billable
: Restored the missing dollar sign in the tasks view.
Services – Validity & Time Zone
: Corrected a date mismatch caused by time zone settings.
Invoices – Categories
: Fixed the invoice category search feature.
Tasks – Schedule
: Addressed a time discrepancy between the list view and task details.