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/repositories/task_template_repo.go

@@ -104,20 +104,6 @@ func (r *TaskTemplateRepository) Count() (int64, error) {
 	return count, err
 }
 
-// GetByRegion returns active templates associated with a specific climate region
-func (r *TaskTemplateRepository) GetByRegion(regionID uint) ([]models.TaskTemplate, error) {
-	var templates []models.TaskTemplate
-	err := r.db.
-		Preload("Category").
-		Preload("Frequency").
-		Preload("Regions").
-		Joins("JOIN task_tasktemplate_regions ON task_tasktemplate_regions.task_template_id = task_tasktemplate.id").
-		Where("task_tasktemplate_regions.climate_region_id = ? AND task_tasktemplate.is_active = ?", regionID, true).
-		Order("task_tasktemplate.display_order ASC, task_tasktemplate.title ASC").
-		Find(&templates).Error
-	return templates, err
-}
-
 // GetGroupedByCategory returns templates grouped by category name
 func (r *TaskTemplateRepository) GetGroupedByCategory() (map[string][]models.TaskTemplate, error) {
 	templates, err := r.GetAll()