Ensure frozen perf uses standard worker size

[bill-ph]

Summary

• pass the deployed standard Duckgres worker CPU and memory into the frozen perf scenario Job
• request that exact worker shape through PGWire startup options so measured queries bypass the exploratory tier
• document worker sizing defaults and add coverage for scenario wiring, Job environment forwarding, and the generated PGWire DSN

Why

Frozen perf connections did not specify a worker profile, so they entered the exploratory tier. Queries that spilled successfully never triggered memory-error escalation and were measured on the small worker instead of the standard worker. Explicit sizing makes the Duckgres and Trino execution-resource comparison stable.

Testing

• just test-unit
• just lint

[github-actions]

Test Impact Plan

Deterministic summary of how this PR changes tests, CI runners, and coverage-risk signals.

Summary

Area	Added	Changed	Deleted
Test files	0	9	0
E2E/journey files	0	0	0
Workflow files	0	0	0

Signals

• Test cases: +0 / -0
• Assertions: +5 / -0
• Skips or known failures added: 0
• Workflow continue-on-error added: 0
• Workflow path filters added: 0
• Test commands removed from justfile: 0
• E2E/journey retry lines added: 0

Coverage risk: neutral or increased

No coverage-reduction warnings detected.