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/services/task_template_service.go

@@ -63,6 +63,26 @@ func (s *TaskTemplateService) GetByID(id uint) (*responses.TaskTemplateResponse,
 	return &resp, nil
 }
 
+// GetByRegion returns templates for a specific climate region.
+// Accepts either a state abbreviation or ZIP code (state takes priority).
+// ZIP codes are resolved to a state via the ZipToState lookup.
+func (s *TaskTemplateService) GetByRegion(state, zip string) ([]responses.TaskTemplateResponse, error) {
+	// Resolve ZIP to state if no state provided
+	if state == "" && zip != "" {
+		state = ZipToState(zip)
+	}
+
+	regionID := GetClimateRegionIDByState(state)
+	if regionID == 0 {
+		return []responses.TaskTemplateResponse{}, nil
+	}
+	templates, err := s.templateRepo.GetByRegion(regionID)
+	if err != nil {
+		return nil, err
+	}
+	return responses.NewTaskTemplateListResponse(templates), nil
+}
+
 // Count returns the total count of active templates
 func (s *TaskTemplateService) Count() (int64, error) {
 	return s.templateRepo.Count()