chore: update RELEASE_NOTES.md with 0.24.2-beta.1 entries

[Aaronontheweb]

Summary

Added 0.24.2-beta.1 release notes to RELEASE_NOTES.md. The GitHub release body was manually corrected (PR #1482 auto-created the release with stale notes from RELEASE_NOTES.md from 0.24.1 instead of pulling from the tag's Directory.Build.props).

This PR syncs the file-based release notes with the tag's PackageReleaseNotes.

Changes since 0.24.1:

• Schema-aware meta argument coercion (Schema-aware coercion of per-call meta arguments (fix Qwen near-miss tool-arg rejections) #1470)
• Per-call meta hint preservation (Schema-aware coercion of per-call meta arguments (fix Qwen near-miss tool-arg rejections) #1470)
• Approval-pause watchdog fix (fix(subagents): honor approval-pause in every tool-watchdog mode #1473)
• Server-feed skill directory mutation blocking (fix(skills): block agent mutations to server feed skill directories #1466)
• Sub-agent spawn lifecycle logging (fix(subagents): record spawn lifecycle in the session transcript #1468)
• OAuth token refresh (fix(providers): refresh inference OAuth tokens #1465)
• LlmSessionActor storage optimization (perf: optimize LlmSessionActor storage to only retain most recent snapshot + last N messages in journal. #1464)
• MessagePack, Anthropic SDK, Aspire.Hosting.Testing bumps (Bump MessagePack from 2.5.301 to 3.1.7 #1420, Bump Anthropic from 12.29.1 to 12.30.0 #1460, Bump Aspire.Hosting.Testing from 13.4.4 to 13.4.6 #1462)