docs: update git workflow to release-based branching

- Rename master to main
- Add release branch workflow (release/vX.Y.Z)
- Feature branches now created from release branches
- Release branches merge to main when confirmed good

CLAUDE.md

@@ -46,10 +46,26 @@ uv run mypy src            # Type check
 
 ## Git Workflow
 
-Trunk-based development with short-lived branches:
+Release-based workflow with feature branches:
 
-- `feature/<story-id>-description` - New features
-- `fix/<description>` - Bug fixes
-- `chore/<description>` - Maintenance
+### Branch Structure
 
-Merge to `main` when complete. Delete branch after merge.
+- `main` - Production-ready code only. Release branches merge here when confirmed good.
+- `release/vX.Y.Z` - Release branches. Created from `main`, feature branches merge here.
+- `feature/<story-id>-description` - Feature branches. Created from a release branch.
+- `fix/<description>` - Bug fix branches. Created from a release branch.
+- `chore/<description>` - Maintenance branches. Created from a release branch.
+
+### Workflow
+
+1. **Start a release**: Create `release/vX.Y.Z` from `main`
+2. **Develop features**: Create `feature/` branches from the release branch
+3. **Complete features**: Merge feature branches back to the release branch
+4. **Ship release**: When release is confirmed good, merge release branch to `main`
+
+### Rules
+
+- Release branches are always created from `main`
+- Feature/fix/chore branches are always created from a release branch
+- Never commit directly to `main`
+- Delete feature branches after merging to release