ci(release): show meaningful release notes on publish

[phuthuycoding]

Summary

The GitHub Release body only said "See CHANGELOG.md for details", forcing readers to open the changelog to find out what shipped. This makes the release notes self-describing.

Changes

• Add "Prepare release notes" step — extracts the newest CHANGELOG.md section (grouped Features / Bug Fixes) into RELEASE_NOTES.md, plus the install command.
• Replace deprecated actions/create-release@v1 with softprops/action-gh-release@v2.
• Enable generate_release_notes: true — GitHub appends "What's Changed" (with PR links), "New Contributors", and the full changelog comparison below the summary.

Result (preview)

## 🚀 Release X.Y.Z
**Release type:** `minor` · **Dist tag:** `latest`
### Install
    npm install moicle@X.Y.Z
### Features
* antigravity: add full skill-based editor support (<commit>)

--- GitHub auto-appends ---
## What's Changed
* <PR title> by @author in #N
## New Contributors / Full Changelog: vA...vB

Matches the standard GitHub release-note format (e.g. the detectIncognito example), instead of a bare changelog link.

🤖 Generated with Claude Code