Messages: permalink, copy link, and embed code #34

Product behaviour (/help/messages)

Every message has a permanent page at /user/<username>/status/<id>. The action bar has a Share button with two options:

• Copy link — the message's permanent address;
• Get embed code — an HTML snippet to paste into a blog post; viewers do not need an account to see an embedded public message.

Only public messages can be linked or embedded for other people; a private message's link and embed work only for the owner while signed in.

Acceptance criteria

• Share action on each feed card with Copy link and Get embed code.
• Both write to the Windows clipboard and confirm in place (non-blocking).
• The permalink resolves to https://interlinedlist.com/user/<username>/status/<id> and opens in the OS browser.
• For a private message, both options are disabled with a note explaining why.