Add task templates API and admin management

- Add TaskTemplate model with category and frequency support
- Add task template repository with CRUD and search operations
- Add task template service layer
- Add public API endpoints for templates (no auth required):
  - GET /api/tasks/templates/ - list all templates
  - GET /api/tasks/templates/grouped/ - templates grouped by category
  - GET /api/tasks/templates/search/?q= - search templates
  - GET /api/tasks/templates/by-category/:id/ - templates by category
  - GET /api/tasks/templates/:id/ - single template
- Add admin panel for task template management (CRUD)
- Add admin API endpoints for templates
- Add seed file with predefined task templates
- Add i18n translations for template errors

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

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

internal/database/database.go

@@ -116,6 +116,7 @@ func Migrate() error {
 		&models.TaskFrequency{},
 		&models.TaskStatus{},
 		&models.ContractorSpecialty{},
+		&models.TaskTemplate{}, // Task templates reference category and frequency
 
 		// User and auth tables
 		&models.User{},