Phase 7D: Frontend deployment guide (Vercel + Netlify)

## Phase 7D — Frontend Deployment Documentation ### Context After running the setup CLI, users need to deploy the React frontend. This is a documentation contribution open to community contributors. ### Scope Write `docs/DEPLOYMENT.md` covering: **1. Vercel (recommended)** - Fork the repo - Connect to Vercel - Set `VITE_SUPABASE_URL` and `VITE_SUPABASE_ANON_KEY` as env vars - Deploy **2. Netlify (alternative)** - Same steps for Netlify **3. Local development** - `npm run dev` in `apps/web` ### Important notes to include - Clearly distinguish VITE_ (public, safe for Vercel) vs non-VITE_ (secrets, must stay in Supabase Vault) - Explain that Open Source Scout does NOT operate a central server — each user's data lives in their own Supabase project ### Acceptance criteria - [ ] `docs/DEPLOYMENT.md` exists - [ ] Vercel steps are documented - [ ] Netlify steps are documented - [ ] Environment variable table is accurate - [ ] Secrets vs public vars are clearly distinguished