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/bmm/workflows/4-implementation/create-story/template.md

@@ -1,49 +0,0 @@
-# Story {{epic_num}}.{{story_num}}: {{story_title}}
-
-Status: ready-for-dev
-
-<!-- Note: Validation is optional. Run validate-create-story for quality check before dev-story. -->
-
-## Story
-
-As a {{role}},
-I want {{action}},
-so that {{benefit}}.
-
-## Acceptance Criteria
-
-1. [Add acceptance criteria from epics/PRD]
-
-## Tasks / Subtasks
-
-- [ ] Task 1 (AC: #)
-  - [ ] Subtask 1.1
-- [ ] Task 2 (AC: #)
-  - [ ] Subtask 2.1
-
-## Dev Notes
-
-- Relevant architecture patterns and constraints
-- Source tree components to touch
-- Testing standards summary
-
-### Project Structure Notes
-
-- Alignment with unified project structure (paths, modules, naming)
-- Detected conflicts or variances (with rationale)
-
-### References
-
-- Cite all technical details with source paths and sections, e.g. [Source: docs/<file>.md#Section]
-
-## Dev Agent Record
-
-### Agent Model Used
-
-{{agent_model_name_version}}
-
-### Debug Log References
-
-### Completion Notes List
-
-### File List