feat(extract): fold HCL block labels into node names

HCL/Terraform blocks were named by their bare keyword, so every resource
collapsed to a single "resource" node and blocks were indistinguishable in the
graph. Fold the quoted labels into the name via the block's string_lit ->
template_literal children, so resource "aws_instance" "web" becomes
resource.aws_instance.web (and variable.region, module.vpc, etc). Each block is
now a distinct, query-friendly Class node. The dedicated terraform parser
(cbm_parse_terraform_source) is unchanged.

Closes #337