docs: add data file documentation and fix data path resolution

All Python cohort scripts now use DATA_DIR = Path(__file__).parent.parent.parent / "data"
to correctly resolve the repo-root data/ directory regardless of the working directory
set by run.sh. All TypeScript scripts have expanded JSDoc headers documenting data file
requirements and environment variables.

python/cohort/remove_resigned_members.py

@@ -6,6 +6,9 @@ before running this script.
 """
 
 import json
+from pathlib import Path
+
+DATA_DIR = Path(__file__).parent.parent.parent / "data"
 
 # Discord IDs of members who have resigned - update before running
 RESIGNED_IDS: list[str] = []
@@ -13,7 +16,7 @@ RESIGNED_IDS: list[str] = []
 
 def main() -> None:
     """Remove resigned members from team assignments."""
-    with open("team_assignments.json") as f:
+    with open(DATA_DIR / "team_assignments.json") as f:
         teams = json.load(f)
 
     changes_made = []
@@ -36,7 +39,7 @@ def main() -> None:
             changes_made.append(f"Removed {removed} participant(s) from {team_name}")
             print(f"⚠️  {team_name}: Proficiency distribution may need updating")
 
-    with open("team_assignments.json", "w") as f:
+    with open(DATA_DIR / "team_assignments.json", "w") as f:
         json.dump(teams, f, indent=2)
 
     if changes_made: