chore: remove orphaned assets and drawio backups (#175)

- Delete git-conflict-markers.drawio (no PNG export, unreferenced)
- Delete project-workflow.png (unreferenced, no drawio source)
- Delete 3 tracked .bkp files (draw.io lock files, already in .gitignore)
- Delete 16 untracked .bkp files from disk

Closes #162

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: braboj