feat: add Terraform/HCL language support (#199)

[stk0vrfl0w]

Adds full .tf / .hcl parsing to code-review-graph, addressing issue #199.

Terraform construct	Node kind	Name
resource "type" "name"	Class	resource.type.name
data "type" "name"	Class	data.type.name
module "name"	Class	module.name
variable "name"	Function	var.name
output "name"	Function	output.name
locals { key = ... }	Function	local.key
provider "name"	Function	provider.name
terraform { ... }	(skipped)

Edge types emitted:

• CONTAINS — file -> every node
• IMPORTS_FROM — file -> module source path (resolved when possible)
• REFERENCES — cross-block value references via variable_expr+get_attr chains

_hcl_variable_refs / _hcl_ref_target resolve dotted expression chains:

• var.x, local.x, module.x, data.type.name -> named graph targets
• resource references (aws_vpc.main.id) -> resource.aws_vpc.main
• Built-in / block-local roots suppressed (no spurious edges): _HCL_REF_PREFIXES includes each, count, self, path, terraform

_HCL_RECURSE_TYPES covers function_call + function_arguments (so var refs inside length(var.x) are extracted) and quoted_template + template_interpolation (so "${var.x}" interpolations are extracted).

_hcl_dynamic_iterator_name() extracts the iterator symbol from any dynamic block (defaulting to the block label; respecting the optional iterator = override). _walk_hcl_expressions accepts a local_names: frozenset[str] scope that accumulates iterator symbols across nested dynamic blocks, suppressing spurious resource..* edges from expressions like setting.value[...] or origin_group.key.

Covers all three cases from the Terraform dynamic-blocks documentation:

• Default iterator (block label = iterator symbol)

• Custom iterator via iterator =

• Multi-level nested dynamic blocks

• code_review_graph/parser.py — extension map, type dicts, 10+ module-level helpers, 4 class methods, _walk_hcl_expressions scope-aware iterator tracking

• tests/fixtures/sample.tf — 243-line fixture covering resources, data sources, modules, variables, outputs, locals, providers, for_each chaining, function-call refs, template interpolations, lifecycle/replace_triggered_by, and all three dynamic block cases

• tests/test_multilang.py — TestHCLParsing: 36 tests, all passing

• docs/FEATURES.md — HCL/Terraform added to language list

• docs/LLM-OPTIMIZED-REFERENCE.md — HCL/Terraform added to

Recognised and fully parsed: Terraform and OpenTofu (.tf, .hcl). OpenTofu is a direct fork of Terraform with identical block schemas.

The following tools also use .hcl files but with different top-level block schemas. Their files will be detected as language="hcl" by extension, but their block types are absent from _HCL_BLOCK_CFG and will produce a File node only (no resources, variables, or edges):

• Terragrunt (terragrunt.hcl, terragrunt.stack.hcl) blocks: include, dependency, dependencies, remote_state, generate, inputs, unit, stack
• Packer (*.pkr.hcl)
  blocks: source, build, packer
• Nomad (*.hcl, *.nomad)
  blocks: job, group, task, service, network
• Vault (*.hcl policy files)
  blocks: path
• Consul (*.hcl config files)
  blocks: datacenter, acl, server, and others
• Waypoint (waypoint.hcl)
  blocks: app, build, deploy, release
• Boundary (*.hcl)
  blocks: controller, worker, listener