chore: upgrade BMAD framework to skill-based architecture

Migrates from slash-command files (.claude/commands, .cursor/commands)
to the new skill-based architecture with workflow step files.

_bmad/tea/workflows/testarch/automate/workflow-plan.md

@@ -1,20 +0,0 @@
-    # Workflow Plan: testarch-automate
-
-    ## Create Mode (steps-c)
-    - step-01-preflight-and-context.md
-
-- step-02-identify-targets.md
-- step-03-generate-tests.md
-- step-04-validate-and-summarize.md
-
-  ## Validate Mode (steps-v)
-  - step-01-validate.md
-
-  ## Edit Mode (steps-e)
-  - step-01-assess.md
-  - step-02-apply-edit.md
-
-  ## Outputs
-  - {test_artifacts}/automation-summary.md
-
-- Test files under {project-root}/tests