docs: add next-release branch workflow to CLAUDE.md

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

CLAUDE.md

@@ -51,6 +51,13 @@ docker build -t paper-dynasty-db .                          # Build image
 - DB connection errors → verify `POSTGRES_HOST` points to correct container name
 - **CI/CD**: Gitea Actions on PR to `main` — builds Docker image, auto-generates CalVer version (`YYYY.MM.BUILD`) on merge
 
+### Release Workflow
+1. Create feature/fix branches off `next-release` (e.g., `fix/card-pricing`)
+2. When done, merge the branch into `next-release` — this is the staging branch where changes accumulate
+3. When ready to release, open a PR from `next-release` → `main`
+4. CI builds Docker image on PR; CalVer tag is created on merge
+5. Deploy the new image to production
+
 ## Important
 
 - Docker image installs only Playwright Chromium (not all browsers) to optimize size