v0.5.3

Documentation correctness follow-up to 0.5.2. No code changes.

• docs/videos/README.md described a CI video-generation job and a GitHub Pages deploy that 0.5.2 removed.
• Feature-video duration comments were measured under CI's software rendering and no longer matched reality (texture-sets claimed ~44s, records 11.5s). They now reflect the local render, along with a note that the duration caps still carry retired CI headroom and are looser than they look.

For Linux users still on 0.5.1 or earlier: self-update was broken before 0.5.2 and the fix ships in it, so one manual update is needed to get back onto the automatic channel.