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_messages.py

@@ -1,10 +1,29 @@
+"""Send initial welcome and roster messages to all team Discord channels.
+
+Creates a pinned roster message in each team channel and stores the resulting
+message ID, channel ID, and role ID in team_message_ids.json for use by
+other scripts (send_checkin.py, update_roster_messages.py, etc.).
+
+Data files (place in data/):
+  - team_assignments.json       Team rosters with leaders and participants per team
+  - applicants_to_evaluate.json  Applicant data including Discord channel/role IDs
+
+Outputs (written to data/):
+  - team_message_ids.json  Channel ID, message ID, and role ID per team
+
+Env vars:
+  - DISCORD_BOT_TOKEN  Bot token for the Discord API
+"""
+
 import json
 import os
 import time
+from pathlib import Path
 
 import requests
 
-# Amari's bot token
+DATA_DIR = Path(__file__).parent.parent.parent / "data"
+
 TOKEN = os.environ["DISCORD_BOT_TOKEN"]
 GUILD_ID = "692816967895220344"
 
@@ -72,12 +91,12 @@ TEAMS = {
 }
 
 # Load team assignments and convert to dict by team name
-with open("team_assignments.json") as f:
+with open(DATA_DIR / "team_assignments.json") as f:
     team_list = json.load(f)
     team_data = {team["name"]: team for team in team_list}
 
 # Load applicants to get project_url by discord_id
-with open("applicants_to_evaluate.json") as f:
+with open(DATA_DIR / "applicants_to_evaluate.json") as f:
     applicants = json.load(f)
     applicant_lookup = {str(a["discord_id"]): a for a in applicants}