docs: add branching model to CONTRIBUTING.md

[jjcav84]

Clarifies that feature and fix PRs should target , while is reserved for tagged stable releases promoted from .

[jjcav84]

Hi maintainers — this is a small docs PR clarifying the -first branching model. Ready for review.

[jjcav84]

@milla-jovovich @igorls this branch is up to date with develop and the full test suite passes. It is ready for final review and merge. @fatkobra if you have bandwidth, a look would be appreciated too.

[fatkobra]

Reviewed and approved.

The new branching guidance is consistent with the repository's existing
contribution flow:

• ordinary feature and fix branches target develop;
• main represents tagged stable releases;
• direct hotfix work is reserved for exceptional release-critical cases.

The examples make the expected base and target branches much clearer without
changing the underlying policy.

[jjcav84]

Merged latest upstream/develop to resolve the UNSTABLE merge state. Branch is now up to date — ready for re-review/approval.

[jjcav84]

Hi @igorls @milla-jovovich — this is a small docs PR clarifying the develop-first branching model in CONTRIBUTING.md. Approved by @fatkobra on Aug 14, rebased onto latest develop on Aug 22. No code changes, no test impact. Ready for merge.