Build load-testing tooling

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Problem: No load-testing tooling exists anywhere in the repository — every existing test is correctness-oriented, none are load- or performance-oriented.

Area: ORB / Scaling

Proposal: Add a load-testing setup (e.g. a scriptable load-generation tool) targeting the Worker's key endpoints, with a documented baseline.

Deliverables:

• A working, repeatable load-test setup and a committed baseline result.

Acceptance criteria:

• The load test can be run on demand and produces a comparable, repeatable throughput/latency number.

AMS Cloud Readiness cross-reference (added 2026-07-12)

See also #5224 in the new AMS Cloud Readiness milestone (#28) — the AMS-side parallel to this exact problem, already citing this issue as precedent. Keep both sides in sync if either design changes.

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JSO-3573

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Releasing from maintainer-only — this milestone is genuinely gated on the undecided 'should we build hosted, and when' question, but this specific issue isn't. Load-testing tooling task (build a scriptable load generator + baseline for the Worker's endpoints) that's useful and runnable regardless of whether hosted ships — no multi-tenant coupling, no business decision, no unreviewed touch to safety-critical state.