fix(assets): remove minimax-output tracking and backup file

- Remove minimax-output/ from git (3.7MB of generation intermediates)
- Add minimax-output/ to .gitignore for future image generation
- Remove apps/web/vitest.config.ts.main.bak backup file
- Finalized demo pet images are already in apps/web/public/demo-pets/

Co-Authored-By: Paperclip <noreply@paperclip.ing>

.gitignore

@@ -7,3 +7,4 @@ dist/
 *.log
 .turbo/
 coverage/
+minimax-output/