Implement independent multi-annotator labeling and adjudication

[alexschmander]

Problem

Labello cannot operationally collect independent labels, calculate agreement, or route disagreements through an authorized adjudication workflow.

Current behavior

Agreement/adjudication shapes and roles exist, but production Adjudicate assignment/UI are disabled and submissions are not isolated as independent candidates.

Desired behavior

Implement the complete independent-labeling, agreement, automatic acceptance, disagreement routing, and adjudication lifecycle.

Acceptance criteria

• Keep annotator submissions isolated until the configured independent-label count is reached.
• Compute configured IoU/keypoint-distance agreement deterministically with versioned policy.
• Automatically finalize agreement and route disagreement to an authorized adjudicator.
• Enable Adjudicate availability, claiming, UI decisions, replay, statistics, and administration.
• Preserve annotator independence, reviewer/adjudicator separation, assignment race safety, and provenance across restart/offline/version migration.

Scope

Cross-cutting domain, storage, API/client, UI, configuration, persistence, and statistics capability.

Implementation notes

Do not enable scaffolded routes/UI until authorization, replay, assignment, and durable data contracts are complete.

Tracking source

docs/tracking/feature-requests.md:19

Independent multi-annotator labeling and adjudication.