[ThinkLinks](https://docs.thinkhead.org/Collaboration/thinklinks) to 2.13 → 2.14 → 2.15.1: mobile hi

Tracking ticket for a line in release 6.3.6.15 that shipped without one.

Upgraded ThinkLinks to 2.13 → 2.14 → 2.15.1: mobile highlighting/notes with a dedicated Notes & Highlights view, background offline downloads, generic OIDC support for self-hosted instances, ~50% lower server memory usage and a 50% smaller Docker image.

Created retroactively so every changelog line has a ticket a reader can follow.