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/responses/task.go

@@ -95,12 +95,22 @@ type TaskResponse struct {
 	IsCancelled     bool                     `json:"is_cancelled"`
 	IsArchived      bool                     `json:"is_archived"`
 	ParentTaskID    *uint        `json:"parent_task_id"`
+	TemplateID      *uint        `json:"template_id,omitempty"` // Backlink to the TaskTemplate this task was created from
 	CompletionCount int          `json:"completion_count"`
 	KanbanColumn    string       `json:"kanban_column,omitempty"` // Which kanban column this task belongs to
 	CreatedAt       time.Time    `json:"created_at"`
 	UpdatedAt       time.Time    `json:"updated_at"`
 }
 
+// BulkCreateTasksResponse is returned by POST /api/tasks/bulk/.
+// All entries are created in a single transaction — if any insert fails the
+// whole batch is rolled back and no partial state is visible.
+type BulkCreateTasksResponse struct {
+	Tasks        []TaskResponse `json:"tasks"`
+	Summary      TotalSummary   `json:"summary"`
+	CreatedCount int            `json:"created_count"`
+}
+
 // Note: Pagination removed - list endpoints now return arrays directly
 
 // KanbanColumnResponse represents a kanban column
@@ -249,6 +259,7 @@ func newTaskResponseInternal(t *models.Task, daysThreshold int, now time.Time) T
 		IsCancelled:     t.IsCancelled,
 		IsArchived:      t.IsArchived,
 		ParentTaskID:    t.ParentTaskID,
+		TemplateID:      t.TaskTemplateID,
 		CompletionCount: predicates.GetCompletionCount(t),
 		KanbanColumn:    DetermineKanbanColumnWithTime(t, daysThreshold, now),
 		CreatedAt:       t.CreatedAt,