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/bmm/docs/images/README.md

@@ -4,7 +4,7 @@
 
 When you edit `workflow-method-greenfield.excalidraw`, regenerate the SVG:
 
-1. Open https://excalidraw.com/
+1. Open <https://excalidraw.com/>
 2. Load the `.excalidraw` file
 3. Click menu (☰) → Export image → SVG
 4. **Set "Scale" to 1x** (default is 2x)