Remove investigation feature completely

- Delete investigation CLI command and related services
- Remove investigation data models and report generators
- Clean up configuration options and documentation
- Update gitignore and remove stale egg-info

Investigation feature is no longer needed and has been fully removed.
Backup preserved in git tag 'pre-investigation-removal'.

config.quickstart.yaml

@@ -35,7 +35,7 @@ tables:
 
 reporting:
   output_dir: "./reports"
-  investigation_dir: "./investigation_reports"
+
   formats:
     html: true
     csv: true