Server-side shared schema draft

[JArmandoAnaya]

A schema draft that lives on the server — composed over several sittings, shared between collaborators, and published as one version when it is ready — instead of today's model where an unpublished class exists only inside one browser tab's dialog session.

Out of scope for the annotation workspace redesign (decision 9). Filed so the constraint it would lift is written down: WS4's Create and add another accumulates classes in component state for the length of one dialog session only, and closing the tab loses them.

cf. #368 (decision 9).

[JArmandoAnaya]

Status correction (2026-08-07): since the draft data-loss fix merged, the
accidental losses this body implies are gone — the Schema tab's draft survives
tab switches and an active-version change under a dirty draft is announced with
an explicit choice instead of a silent overwrite. What remains is exactly one
loss, the deliberate one: dialog-session state (the annotator's
create-and-add-another accumulation) and the Schema tab's local draft still die
with the browser session, by design. That end-of-session loss is the constraint
this issue exists to lift. Urgency unchanged; scope unchanged.

[JArmandoAnaya]

Milestoned 0.1.0 per the default rule (Armando, 2026-08-07): everything lands in 0.1.0 unless explicitly moved.