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/catch_up_report.py

@@ -11,9 +11,12 @@ import json
 import os
 import subprocess
 from datetime import datetime, timezone
+from pathlib import Path
 
 import aiohttp
 
+DATA_DIR = Path(__file__).parent.parent.parent / "data"
+
 DISCORD_BOT_TOKEN = os.environ["DISCORD_BOT_TOKEN"]
 DISCORD_API_BASE = "https://discord.com/api/v10"
 GITHUB_API_BASE = "https://api.github.com"
@@ -440,10 +443,10 @@ def build_report(
 async def main() -> None:
     """Run the catch-up activity report."""
     print("Loading data files...")
-    with open("team_assignments.json") as f:
+    with open(DATA_DIR / "team_assignments.json") as f:
         team_data: list[dict] = json.load(f)
 
-    with open("discord_to_github.json") as f:
+    with open(DATA_DIR / "discord_to_github.json") as f:
         discord_to_github: dict[str, str] = json.load(f)
 
     print("Getting GitHub token via gh CLI...")