fix(session): process pending web retests after ingest

[mikemikimike]

Summary

• Automatically drains pending web retests after the ingest queue finishes.
• Claims pending retests atomically in priority order so concurrent drains cannot duplicate work.
• Keeps queue completion state accurate while retests are being processed and marks failures as completed.
• Adds regression coverage for queue drain ordering, pause/resume behavior, and priority claims.

Fixes #74

Issue: #74

Testing

• bun test --timeout 30000 test/session/ingest-queue-retest.test.ts test/session/web-retest.test.ts (3 behavior tests passed; Windows preload cleanup reports an existing EBUSY after assertions)
• bun test --timeout 30000 test/session/ingest-queue.test.ts (11 existing assertions passed; Windows preload cleanup reports an existing EBUSY after assertions)
• bunx --no-install tsgo --noEmit
• bunx prettier --check src/server/routes/session.ts src/session/ingest-queue.ts src/session/web/web-retest.ts test/session/ingest-queue-retest.test.ts test/session/web-retest.test.ts