Expand .env.example with documentation for all required variables

[happyseaurchin]

Current State

.env.example exists but is minimal. A new contributor cloning the repo doesn't know what keys they need, where to get them, or which are optional.

What's Needed

Expand .env.example with:

• Every environment variable the app uses
• Comments explaining what each one is
• Where to obtain each key (e.g., "Get from Supabase dashboard → Settings → API")
• Which are required vs. optional
• Example format (without actual values)

Example Format

# Supabase — get these from https://supabase.com/dashboard/project/YOUR_PROJECT/settings/api
VITE_SUPABASE_URL=https://your-project.supabase.co
VITE_SUPABASE_ANON_KEY=your-anon-key-here

# Claude API — for LLM edge functions (optional for frontend-only development)
# ANTHROPIC_API_KEY=sk-ant-your-key-here

Labels

documentation good first issue help wanted