[Repo Assist] Release 21.0.1

[github-actions]

🤖 This is an automated PR from Repo Assist, an AI assistant for this repository.

Summary

This PR prepares the 21.0.1 patch release by updating RELEASE_NOTES.md to promote the [Unreleased] content to a versioned release entry.

Changes Included

• Update FCS to 43.10.100 (#966) — already merged to main after the 21.0.0 stable release.

This keeps FSharp.Formatting aligned with the latest F# Compiler Services release.

What This Does

Changing the ## [Unreleased] header to ## 21.0.1 - 2026-02-22 in RELEASE_NOTES.md causes the CI pipeline (push-main.yml) to publish the new NuGet package version when merged.

A fresh empty ## [Unreleased] section is retained at the top for future changes.

Test Status

Build and tests were not run locally (build infrastructure requires NuGet restore and is time-consuming). The CI pipeline will validate this on merge. The change is a one-line header update with no code changes.

Generated by Repo Assist

To install this workflow, run gh aw add githubnext/agentics/workflows/repo-assist.md@077cdbca7864e820e3425e9598cf1269d3dce05a. View source at https://github.com/githubnext/agentics/tree/077cdbca7864e820e3425e9598cf1269d3dce05a/workflows/repo-assist.md.

[github-actions]

✅ Commit pushed: aefee2c

[nojaf]

Could go for minor/major if we bump FCS, not a revision.

[dsyme]

/repo-assist update this PR with latest changes and major version bump