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/dto/requests/task.go

@@ -52,6 +52,18 @@ func (fd *FlexibleDate) ToTimePtr() *time.Time {
 	return &fd.Time
 }
 
+// BulkCreateTasksRequest represents a batch create. Used by onboarding to
+// insert 1-N selected tasks atomically in a single transaction so that a
+// failure halfway through doesn't leave a partial task list behind.
+//
+// ResidenceID is validated once at the service layer; individual task
+// entries must reference the same residence or be left empty (the service
+// overrides each entry's ResidenceID with the top-level value).
+type BulkCreateTasksRequest struct {
+	ResidenceID uint                `json:"residence_id" validate:"required"`
+	Tasks       []CreateTaskRequest `json:"tasks" validate:"required,min=1,max=50,dive"`
+}
+
 // CreateTaskRequest represents the request to create a task
 type CreateTaskRequest struct {
 	ResidenceID        uint             `json:"residence_id" validate:"required"`
@@ -66,6 +78,10 @@ type CreateTaskRequest struct {
 	DueDate            *FlexibleDate    `json:"due_date"`
 	EstimatedCost      *decimal.Decimal `json:"estimated_cost"`
 	ContractorID       *uint            `json:"contractor_id"`
+	// TemplateID links the created task to the TaskTemplate it was spawned from
+	// (e.g. onboarding suggestion or catalog pick). Optional — custom tasks
+	// leave this nil.
+	TemplateID *uint `json:"template_id"`
 }
 
 // UpdateTaskRequest represents the request to update a task