Delegate organization on wikis and snippets so org maintenance mode covers their LFS/Git access

The following discussion from !251067 (merged) should be addressed:

• @chen-gitlab started a discussion:

  Worth a comment noting what this guard intentionally skips, since it reads as though it covers every container:

  • Wiki/ProjectWiki/GroupWiki define no organization method and delegate only run_after_commit, so respond_to? is false and wiki LFS is unenforced — and the routes comment confirms LFS routes are exposed on all repository types
  • Project snippets do respond, but keep organization_id NULL and resolve the org via their project (snippet.rb:36-41), so container.organization is nil and this no-ops

  Are wikis and project snippets deliberately out of scope for this iteration? If they're in scope, a project&.organization fallback should cover both