docs: Add CONTRIBUTING.md and fix README badges

CONTRIBUTING.md

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+# Contributing to SnowTower
+
+## Branch Strategy
+
+SnowTower uses a **release branch** workflow:
+
+```
+feature/* ──► v0.x (release branch) ──► main
+```
+
+### Protected Branches
+
+The following branches are protected and require PRs:
+
+| Branch | Purpose | Protection |
+|--------|---------|------------|
+| `main` | Production releases | PR required, 1 approval, CI must pass |
+| `v*` | Release staging | PR required, 1 approval (automatic via ruleset) |
+
+**You cannot push directly to `main` or release branches.**
+
+> **Note**: Release branches (`v0.2`, `v0.3`, `v1.0`, etc.) are automatically protected by a GitHub ruleset that matches `v*`. New release branches get protection automatically - no manual setup required.
+
+### Workflow
+
+1. **Create feature branch** from the current release branch:
+   ```bash
+   git checkout v0.2
+   git pull origin v0.2
+   git checkout -b feature/my-feature
+   ```
+
+2. **Make changes** and commit:
+   ```bash
+   # Run pre-commit before committing
+   uv run pre-commit run --all-files
+
+   git add .
+   git commit -m "feat: Add my feature"
+   ```
+
+3. **Push and create PR** targeting the release branch:
+   ```bash
+   git push -u origin feature/my-feature
+   gh pr create --base v0.2
+   ```
+
+4. **After PR approval and merge**, changes go to the release branch
+
+5. **When ready to release**, the release branch merges to `main` and gets tagged
+
+## CI Requirements
+
+All PRs must pass CI checks before merging:
+
+- **Lint & Format Check**: `uv run pre-commit run --all-files`
+- **Run Tests**: `uv run pytest`
+
+### Local Verification
+
+Before pushing, always run:
+
+```bash
+# Install pre-commit hooks (one-time)
+uv run pre-commit install
+
+# Run all checks
+uv run pre-commit run --all-files
+uv run pytest
+```
+
+## Commit Messages
+
+Use [Conventional Commits](https://www.conventionalcommits.org/):
+
+```
+feat: Add new feature
+fix: Fix bug
+docs: Update documentation
+style: Format code
+refactor: Refactor code
+test: Add tests
+chore: Maintenance tasks
+```
+
+Examples:
+```bash
+git commit -m "feat: Add user creation workflow"
+git commit -m "fix: Correct warehouse auto-suspend timing"
+git commit -m "docs: Update README badges"
+```
+
+## Pull Request Guidelines
+
+### PR Template
+
+PRs should include:
+- **Summary**: What changed and why
+- **Change Type**: Infrastructure / Code / Documentation / Tests / CI/CD
+- **Related Issues**: Link issues with `Closes #123` or `Fixes #123`
+- **Test Plan**: How you verified the changes
+- **Checklist**: Pre-commit passes, no secrets, tests pass
+
+### Linking to Issues
+
+When your PR addresses an issue, use closing keywords:
+```markdown
+Closes #123
+Fixes #456
+```
+
+This automatically closes the issue when the PR is merged.
+
+## Release Process
+
+1. **All features merged** to release branch (e.g., `v0.2`)
+2. **Final testing** on release branch
+3. **Create PR** from release branch to `main`
+4. **Merge and tag**:
+   ```bash
+   git checkout main
+   git pull
+   git tag v0.2.0
+   git push origin v0.2.0
+   ```
+5. **Release workflow** automatically creates GitHub Release
+
+## What NOT to Do
+
+- **Don't push directly** to `main` or release branches
+- **Don't force push** to protected branches
+- **Don't skip pre-commit** hooks
+- **Don't merge without CI passing**
+- **Don't include secrets** in commits (credentials, API keys, etc.)
+
+## Getting Help
+
+- **Issues**: [Open an issue](https://github.com/Database-Tycoon/SnowTower/issues/new/choose)
+- **Discussions**: Use GitHub Discussions for questions