chore: remove old KCTCS data files and merge script

[William-Hill]

Closes #43

Summary

• Remove 7 KCTCS CSV files from data/ (~205 MB tracked data):
  • ar_kcts_with_zip.csv
  • kctcs_cohorts_with_zip.csv
  • kctcs_courses.csv
  • kctcs_merged_with_predictions.csv
  • kctcs_merged_with_zip.csv
  • kctcs_student_level_with_predictions.csv
  • kctcs_student_level_with_zip.csv
• Remove ai_model/merge_kctcs_data.py (superseded by merge_bishop_state_data.py)
• Delete database_dumps/dump-Kentucky_Community_and_Technical_College_System.sql locally (609 MB MariaDB dump, was never tracked by git)

Remaining data files

data/
├── ar_bscc_with_zip.csv
├── bishop_state_cohorts_with_zip.csv
├── bishop_state_courses.csv
├── bishop_state_student_level_with_zip.csv
├── De-identified PDP AR Files.xlsx
└── README.md

Test plan

• data/ contains only Bishop State files
• ai_model/merge_kctcs_data.py is gone; merge_bishop_state_data.py remains
• No KCTCS CSV references remain in tracked files