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/send_checkin.py

@@ -1,11 +1,25 @@
-"""Send check-in messages to all team channels."""
+"""Send biweekly check-in messages to all team Discord channels.
+
+Posts a check-in prompt to each team channel and automatically creates a thread
+for responses. Members who do not respond by the deadline may be removed for
+inactivity.
+
+Data files (place in data/):
+  - team_message_ids.json  Channel IDs per team (generated by send_team_messages.py)
+
+Env vars:
+  - DISCORD_BOT_TOKEN  Bot token for the Discord API
+"""
 
 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"]
 DISCORD_API = "https://discord.com/api/v10"
 GUILD_ID = "692816967895220344"
@@ -22,7 +36,7 @@ CHECK_IN_MESSAGE = """@everyone it is time for Naomi to do a check in. I need **
 
 async def send_checkin_to_teams() -> None:
     """Send check-in message to all team channels (except Jade Jasmine)."""
-    with open("team_message_ids.json") as f:
+    with open(DATA_DIR / "team_message_ids.json") as f:
         team_data = json.load(f)
 
     headers = {