Submit Sharded Throughput Default

Motivation

The BLAST submit runtime panel could show prepared shards and safe capacity while keeping the run profile on Warmed database. That made the default selection contradict the availability message.

User-facing change

When a selected database is already warm, has prepared shards, and fits the selected cluster, the submit form now promotes the run profile to Sharded throughput automatically. If the user explicitly chooses Off, Baseline, or Warmed database, that opt-out is preserved.

API/IaC diff summary

No API or IaC changes. Frontend-only reconciliation of submit runtime form state.

Validation evidence

• npm run test -- shardingAvailability.test.ts --run in web/.
• npm run build in web/.