Fix QA checklist: accept default terraform.tfstate, remove stale state path convention

QA still had the old stage-N-slug.tfstate checklist item (line 263)
causing false CRITICAL on every stage. Updated to accept backend local {}
and default terraform.tfstate. Updated remote state defaults to use
relative paths (../stage-N-name/terraform.tfstate).

Full audit confirmed no other stale references to .terraform-state/ or
stage-N-slug convention remain in code, governance, or tests.

Author: a11smiles

azext_prototype/agents/builtin/qa_engineer.py

@@ -260,7 +260,8 @@ def _encode_image(path: str) -> str:
 - [ ] providers.tf includes `required_version = ">= 1.9.0"`
 - [ ] main.tf does NOT contain terraform {} or provider {} blocks
 - [ ] All .tf files are syntactically valid HCL (properly opened/closed blocks)
-- [ ] Backend state file path follows convention: `stage-{N}-{slug}.tfstate`
+- [ ] Backend `backend "local" {}` is acceptable — each stage uses default `terraform.tfstate`
+      in its own directory. Do NOT flag empty backend or `terraform.tfstate` as an issue.
 
 ### 8. CRITICAL: Scope Compliance
 - [ ] No resources created that are not listed in "Services in This Stage"
@@ -290,7 +291,7 @@ def _encode_image(path: str) -> str:
 - [ ] Cross-stage references use the **exact** output key names listed in the
       "Previously Generated Stages" section — do **NOT** flag keys as "non-standard"
       if they match what the upstream stage _actually_ exports
-- [ ] Remote state variable defaults match upstream backend paths exactly
+- [ ] Remote state variable defaults use relative paths: `../stage-N-name/terraform.tfstate`
 - [ ] **NO** unused `terraform_remote_state` data sources — every data source
       **MUST** have at least one output referenced in locals or resources
 - [ ] **NO** unused variables for state paths — if the data source is removed,