Add regional task templates API with climate zone lookup

Adds a new endpoint GET /api/tasks/templates/by-region/?zip= that resolves
ZIP codes to IECC climate regions and returns relevant home maintenance
task templates. Includes climate region model, region lookup service with
tests, seed data for all 8 climate zones with 50+ templates, and OpenAPI spec.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

internal/dto/responses/task_template.go

@@ -21,6 +21,8 @@ type TaskTemplateResponse struct {
 	Tags         []string               `json:"tags"`
 	DisplayOrder int                    `json:"display_order"`
 	IsActive     bool                   `json:"is_active"`
+	RegionID     *uint                  `json:"region_id,omitempty"`
+	RegionName   string                 `json:"region_name,omitempty"`
 	CreatedAt    time.Time              `json:"created_at"`
 	UpdatedAt    time.Time              `json:"updated_at"`
 }
@@ -63,6 +65,11 @@ func NewTaskTemplateResponse(t *models.TaskTemplate) TaskTemplateResponse {
 		resp.Frequency = NewTaskFrequencyResponse(t.Frequency)
 	}
 
+	if len(t.Regions) > 0 {
+		resp.RegionID = &t.Regions[0].ID
+		resp.RegionName = t.Regions[0].Name
+	}
+
 	return resp
 }