docs: clean up sync example, add team sync section to README

Remove _comment hacks from JSON example file. Add short team sync
section to README explaining what it is, that it's optional, and
how to set it up.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

.gstack-sync.json.example

@@ -1,9 +1,4 @@
 {
-  "_comment": "OPTIONAL: Team sync configuration for shared eval/retro/QA data via Supabase.",
-  "_docs": "See docs/designs/TEAM_COORDINATION_STORE.md for full setup guide.",
-  "_what_you_get": "Shared eval dashboards, cross-team trend tracking, retro aggregation, QA report history. Without this file, everything works locally — sync is purely additive.",
-  "_setup": "1. Create a Supabase project. 2. Run supabase/migrations/*.sql in order. 3. Copy this file to .gstack-sync.json and fill in your values. 4. Set GSTACK_SUPABASE_ACCESS_TOKEN or run gstack sync login.",
-
   "supabase_url": "https://YOUR_PROJECT.supabase.co",
   "supabase_anon_key": "eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.YOUR_ANON_KEY_HERE",
   "team_slug": "your-team-name"

README.md

@@ -629,6 +629,12 @@ bun run eval:watch            # live dashboard during E2E runs
 
 E2E tests stream real-time progress, write machine-readable diagnostics, and persist partial results that survive kills. See CONTRIBUTING.md for the full eval infrastructure.
 
+### Team sync (optional)
+
+For teams, gstack can sync eval results, retro snapshots, QA reports, and ship logs to a shared Supabase store. Without this, everything works locally as before — sync is purely additive.
+
+To set up: copy `.gstack-sync.json.example` to `.gstack-sync.json`, create a Supabase project, run the migrations in `supabase/migrations/`, and fill in your credentials. See `docs/designs/TEAM_COORDINATION_STORE.md` for the full guide.
+
 ## License
 
 MIT