Onboarding: template backlink, bulk-create endpoint, climate-region scoring

Clients that send users through a multi-task onboarding step no longer
loop N POST /api/tasks/ calls and no longer create "orphan" tasks with
no reference to the TaskTemplate they came from.

Task model
- New task_template_id column + GORM FK (migration 000016)
- CreateTaskRequest.template_id, TaskResponse.template_id
- task_service.CreateTask persists the backlink

Bulk endpoint
- POST /api/tasks/bulk/ — 1-50 tasks in a single transaction,
  returns every created row + TotalSummary. Single residence access
  check, per-entry residence_id is overridden with batch value
- task_handler.BulkCreateTasks + task_service.BulkCreateTasks using
  db.Transaction; task_repo.CreateTx + FindByIDTx helpers

Climate-region scoring
- templateConditions gains ClimateRegionID; suggestion_service scores
  residence.PostalCode -> ZipToState -> GetClimateRegionIDByState against
  the template's conditions JSON (no penalty on mismatch / unknown ZIP)
- regionMatchBonus 0.35, totalProfileFields 14 -> 15
- Standalone GET /api/tasks/templates/by-region/ removed; legacy
  task_tasktemplate_regions many-to-many dropped (migration 000017).
  Region affinity now lives entirely in the template's conditions JSON

Tests
- +11 cases across task_service_test, task_handler_test, suggestion_
  service_test: template_id persistence, bulk rollback + cap + auth,
  region match / mismatch / no-ZIP / unknown-ZIP / stacks-with-others

Docs
- docs/openapi.yaml: /tasks/bulk/ + BulkCreateTasks schemas, template_id
  on TaskResponse + CreateTaskRequest, /templates/by-region/ removed

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

internal/services/task_template_service.go

@@ -63,26 +63,6 @@ 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()