Add git workflow rules to CLAUDE.md

Never work on main directly; always switch back to development after
merging to main.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

CLAUDE.md

@@ -70,3 +70,9 @@ Dashboard has a chart toggle (Both / Portfolio / 1-Year BTC) using tab state in
 - `purchases`: id, amount_eur, price_eur, created_at, user_id (FK)
 
 Database persists via Docker volume at `/app/data/btc_portfolio.db`.
+
+## Git Workflow
+
+- **Never work directly on `main`.** All development happens on `development` (or a feature branch).
+- After any merge/push to `main`, always switch back to `development` immediately.
+- `main` is only touched to merge in completed work from `development`.