[FEATURE]: make `opncd.ai/share` urls return the full session as md/json when fetched by agents

[remorses]

Feature hasn't been suggested before.

• I have verified this feature I'm about to request hasn't been suggested before.

Describe the enhancement you want to request

Now opencode share urls depend on client side javascript to render all the content. This is problematic when fetched by agents. which do not see anything

A solution would be to make them server render when fetched with an agent user-agent header.

Or at least return them as .json, returning the session data (which is already available and would be an easy fix)