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/update_roster_messages.py

@@ -3,9 +3,12 @@
 import asyncio
 import json
 import os
+from pathlib import Path
 
 import aiohttp
 
+DATA_DIR = Path(__file__).parent.parent.parent / "data"
+
 DISCORD_BOT_TOKEN = os.environ["DISCORD_BOT_TOKEN"]
 GUILD_ID = "692816967895220344"
 
@@ -62,13 +65,13 @@ def generate_roster(team: dict, discord_to_github: dict) -> str:
 
 async def main() -> None:
     """Update roster messages for all teams."""
-    with open("team_message_ids.json") as f:
+    with open(DATA_DIR / "team_message_ids.json") as f:
         team_data = json.load(f)
 
-    with open("team_assignments.json") as f:
+    with open(DATA_DIR / "team_assignments.json") as f:
         teams = json.load(f)
 
-    with open("discord_to_github.json") as f:
+    with open(DATA_DIR / "discord_to_github.json") as f:
         discord_to_github = json.load(f)
 
     async with aiohttp.ClientSession() as session: