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_team_checkin.py

@@ -1,12 +1,26 @@
 #!/usr/bin/env python3
-"""Send team check-in messages to all 14 teams."""
+"""Send a capacity check-in message to each team channel.
+
+Posts a message asking whether the team feels able to complete their project
+given their current member count, and invites them to request support if needed.
+
+Data files (place in data/):
+  - team_message_ids.json   Channel and role IDs per team (from send_team_messages.py)
+  - team_assignments.json   Team rosters used to report current member counts
+
+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"]
 NAOMI_ID = "465650873650118659"
 
@@ -58,10 +72,10 @@ async def send_message(
 
 async def main() -> None:
     """Send check-in messages to 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)
 
     async with aiohttp.ClientSession() as session: