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/router/router.go

@@ -515,7 +515,8 @@ func setupPublicDataRoutes(api *echo.Group, residenceHandler *handlers.Residence
 		templates.GET("/grouped/", taskTemplateHandler.GetTemplatesGrouped)
 		templates.GET("/search/", taskTemplateHandler.SearchTemplates)
 		templates.GET("/by-category/:category_id/", taskTemplateHandler.GetTemplatesByCategory)
-		templates.GET("/by-region/", taskTemplateHandler.GetTemplatesByRegion)
+		// /by-region/ removed — climate zone now participates in the main
+		// GET /api/tasks/suggestions/ scoring via the template JSON conditions.
 		templates.GET("/:id/", taskTemplateHandler.GetTemplate)
 	}
 }
@@ -550,6 +551,7 @@ func setupTaskRoutes(api *echo.Group, taskHandler *handlers.TaskHandler) {
 	{
 		tasks.GET("/", taskHandler.ListTasks)
 		tasks.POST("/", taskHandler.CreateTask)
+		tasks.POST("/bulk/", taskHandler.BulkCreateTasks)
 		tasks.GET("/by-residence/:residence_id/", taskHandler.GetTasksByResidence)
 
 		tasks.GET("/:id/", taskHandler.GetTask)