🚀 Prepare release of v1.0.1

[flowerthrower]

Description

This PR:

• adds the v1.0.1 changelog section with the release date;
• adds missing upgrade guide with v1.0.1 and v1.0.0 sections;
• updates version links for v1.0.1;

Checklist

• The pull request only contains commits that are focused and relevant to this change.
• I have added appropriate tests that cover the new/changed functionality.
• I have updated the documentation to reflect these changes.
• I have added entries to the changelog for any noteworthy additions, changes, fixes, or removals.
• I have added migration instructions to the upgrade guide (if needed).
• The changes follow the project's style guidelines and introduce no new warnings.
• The changes are fully tested and pass the CI checks.
• I have reviewed my own code changes.

If PR contains AI-assisted content:

• I have disclosed the use of AI tools in the PR description as per our AI Usage Guidelines.
• AI-assisted commits include an Assisted-by: GPT-5 via Codex footer.
• I confirm that I have personally reviewed and understood all AI-generated content, and accept full responsibility for it.

Assisted-by: GPT-5.5 via Codex

[burgholzer]

Just some (hopefully minor) request for changes here.

[burgholzer]

LGTM modulo some minor tweaks