[feature]: (#496) Prevent Duplicate service template task from creation

[Rakeshsingu]

Feature: Prevent Duplicate Task Creation for Specific Task Types During Service Template Task Generation

When a Repair Order (Project) has multiple linked Service Templates (e.g. PPF, Tinting),
it's possible for tasks with the same task_type (e.g. "Washing") to appear in multiple templates.

To avoid creating duplicate tasks for such cases, this update introduces:

✅ New Field:

• prevent_duplicate_task: A checkbox in the Service Template's tasks child table.

💡 Logic:

• During task creation (create_service_template_tasks):

  1. Collect all task_types where prevent_duplicate_task = 1 from all service templates.
  2. Fetch existing task_types already created for the project.
  3. While iterating tasks:
     • If the task's task_type is in the prevent_duplicate_task list
     • And it already exists in the project (either from the DB or created in this run)
     • ❌ Skip creating that task.

• Only the first occurrence of such a task type will be created.

• Ensures clean deduplication across all service templates attached to the same project.

🛠️ Example:

If both "PPF" and "Tinting" templates have a "Washing" task with prevent_duplicate_task = 1,
only the first "Washing" task is created; the duplicate is skipped.

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This prevents redundant tasks from being added to the same Repair Order, improving task clarity and reducing confusion for workshop staff.

Closes #496