Self-documenting bot comment: include the add-more-media command

[zachdunn]

Self-documenting bot comment: include the "add more media" command

The managed uploads-sh[bot] attachments comment (#290) lists what's been uploaded for a PR/issue, but a reader has no in-context hint for how to add to it. Include a short, copy-pasteable command in the comment footer, e.g.:

Add media: uploads put <file> --pr <N> --comment   (or --issue <N>)

• Keep it generic — repo + number only, never a workspace name or token.
• Small render-only change to the shared comment body (mirrored in both the api and CLI renderers, guarded by the golden fixture).

Prerequisite: authorization (#297)

Publishing the command in a public comment invites anyone to run it, which makes the cross-tenant authorization gap (#297) materially worse: a stranger with any workspace could follow the printed command to post into / overwrite this PR's bot comment. This feature should land after #297, so that the endpoint enforces who may post before we advertise how.

Open questions

• Show galleries/attach variants too, or just the core put --comment?
• Only render the command when the viewer could plausibly act (hard in a static comment) — or accept that it's informational and rely on Cross-tenant authorization for the bot-comment endpoint (workspace may target any org's repo) #297 for enforcement (preferred).