docs: update CONTRIBUTING with v2 branching strategy

Clarify that main is now the v2 development branch where breaking
changes are welcome, and v1.x is the maintenance branch for security
and critical bug fixes only.

Author: maxisbey

CONTRIBUTING.md

@@ -23,9 +23,14 @@ uv tool install pre-commit --with pre-commit-uv --force-reinstall
 ## Development Workflow
 
 1. Choose the correct branch for your changes:
-   - For bug fixes to a released version: use the latest release branch (e.g. v1.1.x for 1.1.3)
-   - For new features: use the main branch (which will become the next minor/major version)
-   - If unsure, ask in an issue first
+
+   | Change Type | Target Branch | Example |
+   |-------------|---------------|---------|
+   | New features, breaking changes | `main` | New APIs, refactors |
+   | Security fixes for v1 | `v1.x` | Critical patches |
+   | Bug fixes for v1 | `v1.x` | Non-breaking fixes |
+
+   > **Note:** `main` is the v2 development branch. Breaking changes are welcome on `main`. The `v1.x` branch receives only security and critical bug fixes.
 
 2. Create a new branch from your chosen base branch