v0.162.0: Release: primary domain migration to strummy.online

Summary

• Promotes main to production — deploys to strummy.online.
• Includes: student sidebar regrouping fix (#578), primary domain migration from strummy.vercel.app/strummy.app to strummy.online (#579).

What changes for users

• The app is now reachable at strummy.online (old strummy.vercel.app and guitar-crm.vercel.app URLs redirect there automatically).
• Sidebar for students now groups My Lessons/My Assignments/My Repertoire under Learning, and Song Library/Theory under a new Resources section.

Test plan

• After merge, confirm strummy.online serves the new production deployment
• Confirm an invite email's accept link resolves correctly on strummy.online

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Full Changelog: v0.161.3...v0.162.0