Resume for every agent

Resume works for every agent now, not only claude

Resume was greyed out whenever sessionhub knew of no session in the folder. For
claude that is a fact about the folder. For codex, omp, or any agent you
add yourself it is a fact about sessionhub — it reads claude's and pi's session
files and asks opencode's CLI, and knows nothing whatever about the rest. So
their Resume button was dead permanently, however many sessions they had.

Both of them have a perfectly good picker of their own. Read off each CLI's own
--help:

codex resume [SESSION_ID]    picker by default
omp -r, --resume=<value>     by ID prefix, path, or picker if omitted

Neither was recorded in the config, so sessionhub had nothing to offer. Both are
filled in on the next start, the same way opencode got --continue.

The row also stops claiming no history here for an agent whose history it
cannot read. Those say ask codex instead, and the button opens the agent's own
list.

A resume that named no session

resume_args of ["resume"] and ["--resume"] do not name a session, so every
session in the sidebar built the same command and the agent opened whichever it
felt like. Corrected to ["resume", "{session_id}"] and
["--resume", "{session_id}"].

Settings now says so for any agent whose resume arguments have no
{session_id} — the next one you add by hand would have hit the same trap
silently.

Also

codex gains codex fork [SESSION_ID], so forking a session works there too. Its
--help lists no flag for naming the forked session, so the panel does not
offer to name one.