chore: remove BMAD framework files and IDE configuration artifacts

Clean up unused BMAD workflow, agent, and command files across all IDE
configurations (.agent, .clinerules, .cursor, .gemini, .github, .kilocode,
.opencode) and internal module files (_bmad/bmb, _bmad/bmm).

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

.github/skills/bmad-agent-tech-writer/explain-concept.md

@@ -0,0 +1,20 @@
+---
+name: explain-concept
+description: Create clear technical explanations with examples
+menu-code: EC
+---
+
+# Explain Concept
+
+Create a clear technical explanation with examples and diagrams for a complex concept.
+
+## Process
+
+1. **Understand the concept** — Clarify what needs to be explained and the target audience
+2. **Structure** — Break it down into digestible sections using a task-oriented approach
+3. **Illustrate** — Include code examples and Mermaid diagrams where helpful
+4. **Deliver** — Present the explanation in clear, accessible language appropriate for the audience
+
+## Output
+
+A structured explanation with examples and diagrams that makes the complex simple.