chore: Clean up temporary planning files and add .ruff_cache to gitignore

Remove temporary project planning files now that quality transformation is complete:
- task_plan.md (temporary project planning)
- progress.md (temporary progress tracking)
- findings.md (temporary research notes)

Add .ruff_cache/ to .gitignore to prevent tracking linter cache files.

These files served their purpose during the quality transformation project
and are no longer needed in the repository.

Author: robotlearning123

.gitignore

@@ -147,3 +147,4 @@ Thumbs.db
 # Generated reports
 reports/*
 !reports/README.md
+.ruff_cache/