feat(quality): add markdownlint-cli2 to quality checks (#1039)

- Add markdownlint-cli2 as dev dependency
- Add lint:md script to package.json
- Add markdownlint job to CI workflow
- Configure 5 rules: heading-increment, no-duplicate-heading,
  no-trailing-punctuation, no-bare-urls, no-space-in-emphasis
- Fix existing violations across 19 markdown files
- No auto-fix to prevent destructive changes

Closes #1034

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

src/modules/bmb/workflows/edit-workflow/steps/step-04-validate.md

@@ -152,7 +152,7 @@ Then load and append content from {completionTemplate}
 
 Display: **Select an Option:** [A] Advanced Elicitation [P] Party Mode [C] Continue
 
-#### EXECUTION RULES:
+### EXECUTION RULES:
 
 - ALWAYS halt and wait for user input after presenting menu
 - ONLY proceed to next step when user selects 'C'