Add Creative Writing expansion pack (#414)

* Add Creative Writing expansion pack
- 10 specialized writing agents for fiction and narrative design
- 8 complete workflows (novel, screenplay, short story, series)
- 27 quality checklists for genre and technical validation
- 22 writing tasks covering full creative process
- 8 professional templates for structured writing
- KDP publishing integration support

* Fix bmad-creative-writing expansion pack formatting and structure

- Convert all agents to standard BMAD markdown format with embedded YAML
- Add missing core dependencies (create-doc, advanced-elicitation, execute-checklist)
- Add bmad-kb.md customized for creative writing context
- Fix agent dependency references to only include existing files
- Standardize agent command syntax and activation instructions
- Clean up agent dependencies for beta-reader, dialog-specialist, editor, genre-specialist, narrative-designer, and world-builder

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Co-authored-by: Brian <bmadcode@gmail.com>

expansion-packs/bmad-creative-writing/checklists/ya-appropriateness-checklist.md

@@ -0,0 +1,16 @@
+# ------------------------------------------------------------
+# 20. YA Appropriateness Checklist
+# ------------------------------------------------------------
+---
+checklist:
+  id: ya-appropriateness-checklist
+  name: Young Adult Content Appropriateness Checklist
+  description: Ensure themes, language, and content suit YA audience.
+items:
+  - "[ ] Protagonist age 13–18 and driving action"
+  - "[ ] Themes of identity, friendship, coming‑of‑age present"
+  - "[ ] Romance handles consent and boundaries responsibly"
+  - "[ ] Violence and language within YA market norms"
+  - "[ ] No explicit sexual content beyond fade‑to‑black"
+  - "[ ] Hopeful or growth‑oriented ending"
+...