Strengthen marimo UI and remote media guidance

[ktaletsk]

Summary

This follow-up captures issues found while repairing and validating the Log
(Almost) Anything notebook in #652:

• preserve a user-designated live or exported molab notebook as the current
  implementation state, including cell order, identifiers, and hide_code
• preserve readable teaching names; use private names only for actual
  cross-cell collisions or implementation-only plumbing
• require widgets to render from their definition cells and use documented
  reactive state such as .value, not invented attributes such as .clicked
• require a fresh post-edit runtime smoke test because marimo check cannot
  detect invisible widgets or invalid runtime attributes
• document YouTube iframe embeds and the tested W&B light/dark logo pair
• preserve a working fsspec backend; use GitHubFS for repository browsing and
  raw HTTPS when a demonstrated API-limit or known-file use case calls for it
• document in-memory W&B adapters for MP4, audio, HTML, and OBJ content
• preserve an existing tutorial ending instead of requiring generic
  verification and next-step prose
• keep live credentials, remote writes, commits, pushes, and PR changes behind
  explicit user authorization

Why

The saved conversion check for the notebook predated a later cleanup pass.
That cleanup still passed without fresh runtime validation, leaving controls
invisible, .clicked references broken, duplicated public names, and local
asset paths unavailable in molab.

Subsequent live validation also showed that cleanup guidance must preserve
working notebook choices instead of applying speculative rewrites. GitHubFS
worked with repository-relative paths and provided browsable remote storage;
bare HTTPFS could open concrete URLs but could not list a root. The final molab
artifact also restored readable teaching names and retained intentional
hide_code settings.

Validation

• skill validator: Skill is valid!
• git diff --check
• independent forward test of the updated preservation, filesystem, naming,
  authorization, and logo guidance

This PR is intentionally stacked on wandbify_skills / #647.