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/handlers/task_handler.go

@@ -151,6 +151,31 @@ func (h *TaskHandler) CreateTask(c echo.Context) error {
 	return c.JSON(http.StatusCreated, response)
 }
 
+// BulkCreateTasks handles POST /api/tasks/bulk/ for onboarding and other
+// flows that need to insert 1-N tasks atomically. The entire batch either
+// commits or rolls back; clients never see a partial state.
+func (h *TaskHandler) BulkCreateTasks(c echo.Context) error {
+	user, err := middleware.MustGetAuthUser(c)
+	if err != nil {
+		return err
+	}
+	userNow := middleware.GetUserNow(c)
+
+	var req requests.BulkCreateTasksRequest
+	if err := c.Bind(&req); err != nil {
+		return apperrors.BadRequest("error.invalid_request")
+	}
+	if err := c.Validate(&req); err != nil {
+		return err
+	}
+
+	response, err := h.taskService.BulkCreateTasks(&req, user.ID, userNow)
+	if err != nil {
+		return err
+	}
+	return c.JSON(http.StatusCreated, response)
+}
+
 // UpdateTask handles PUT/PATCH /api/tasks/:id/
 func (h *TaskHandler) UpdateTask(c echo.Context) error {
 	user, err := middleware.MustGetAuthUser(c)