chore(assets): retire unreferenced binary files

Remove four unreferenced binary assets from the live site and prevent accidental recommit while preserving historical recoverability until the controlled mirror/archive step.

Author: DataForSolution

.gitignore

@@ -20,3 +20,7 @@ toolkits/cheatsheets/Pandas_Cheat_Sheet.pdf
 toolkits/cheatsheets/Python_Cheat_Sheet.pdf
 toolkits/cheatsheets/Scikit_Learn_Cheat_Sheet_Python.pdf
 toolkits/notebooks/Chest_CT-Scan-CNN-Project.ipynb
+assets/documents/chest-cancer-detection.pdf
+assets/videos/background-video.mp4
+assets/videos/llmachine.mp4
+assets/toolkits/study_planners/ML_Study_Planner_60Days.pdf