Post-overhaul UX, performance, and cleanup triage

This issue collects deliberately deferred work discovered during the lifecycle-overhaul final audit. None of it is required for the initial release unless separately promoted into the authoritative completion plan.

Submission experience

• Add a submit call-to-action on problem pages and a searchable problem selector.
• Accept convenient repository URLs/refs, resolve them to immutable commits, and ask the submitter to confirm the resolved commit.
• Add optional friendly metadata fields and a preview of the public submission/result presentation.
• Add a durable receipt/status page with useful progress information.
• Replace the current inferred OAuth state with an explicit server-confirmed signed-in state.
• Guide users through missing GitHub App access; reconsider consolidating the two app installations.
• Improve form styling and human-readable display of submission metadata.

Reliability and operations

• Display a stale-data warning on the public site and alert operators when publication stops advancing.
• Profile and reduce evaluation latency, including cache behavior, nanoda runtime, the six-hour ceiling, and memory/OOM behavior. Keep the existing generator, latency, nanoda, and OOM issues linked to this work rather than duplicating them.
• Reduce contention in State result callbacks.
• Profile and reduce the roughly 20-minute leaderboard Pages build so small copy and projection fixes do not dominate deployment wall-clock.
• Make cross-repository State contract rollouts avoid a production-disabled gap: validate the candidate contract before disabling the current Worker or restore the prior healthy version on pre-finalization failure.

Post-transition cleanup

• Delete one-shot migration machinery after the final issue-intake delta is complete.
• Simplify release automation after the post-embargo production canary.
• Split the large submission workflow, Worker application, and GitHub-backed state implementation into smaller maintainable units.
• Eventually delete disabled publication opt-out/revocation and model-consolidation code paths.

Issue hygiene after launch

• Close or reclassify stale/fixed reports, including lean-eval #511, lean-eval-leaderboard #53 and #64, the FC-related lean-eval #533, model-consolidation lean-eval-leaderboard #83, and orphaned lean-eval-submissions #585 and #1449.
• Link the existing generator, latency, nanoda, and OOM issues here once triage begins.

Calendar-bound cutoff, retirement, and canary work stays in the overhaul execution runbook and its existing PRs; it is intentionally not duplicated here.

This is a cross-cutting triage list rather than a self-contained change. Start by comparing its deferred items with the authoritative completion plan, existing generator, latency, nanoda, and OOM issues, and the post-overhaul runbook. It is done when each item is split or linked to a scoped issue, with stale work reclassified and calendar-bound work left in the runbook.