chore: add VSCode settings and update README.md (markdown-lint) (#209)

* chore: add VSCode settings and update README for clarity**

### CHANGES
- Add recommended extensions for VSCode in `extensions.json`
- Create `settings.json` for custom spell-checker words
- Update README to specify plaintext in code block

* chore: add other technical words to cspell dictionary

---------

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

README.md

@@ -70,7 +70,7 @@ npm run validate       # Validate configurations
 
 ## Project Structure
 
-```
+```plaintext
 .bmad-core/
 ├── agents/          # Individual agent definitions
 ├── agent-teams/     # Team configurations