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/models/task_template.go

@@ -0,0 +1,22 @@
+package models
+
+// TaskTemplate represents a predefined task template that users can select when creating tasks
+type TaskTemplate struct {
+	BaseModel
+	Title           string        `gorm:"column:title;size:200;not null" json:"title"`
+	Description     string        `gorm:"column:description;type:text" json:"description"`
+	CategoryID      *uint         `gorm:"column:category_id;index" json:"category_id"`
+	Category        *TaskCategory `gorm:"foreignKey:CategoryID" json:"category,omitempty"`
+	FrequencyID     *uint         `gorm:"column:frequency_id;index" json:"frequency_id"`
+	Frequency       *TaskFrequency `gorm:"foreignKey:FrequencyID" json:"frequency,omitempty"`
+	IconIOS         string        `gorm:"column:icon_ios;size:100" json:"icon_ios"`
+	IconAndroid     string        `gorm:"column:icon_android;size:100" json:"icon_android"`
+	Tags            string        `gorm:"column:tags;type:text" json:"tags"` // Comma-separated tags for search
+	DisplayOrder    int           `gorm:"column:display_order;default:0" json:"display_order"`
+	IsActive        bool          `gorm:"column:is_active;default:true;index" json:"is_active"`
+}
+
+// TableName returns the table name for GORM
+func (TaskTemplate) TableName() string {
+	return "task_tasktemplate"
+}