chore(deps): upgrade Jest past 26 to drop deprecated request/jsdom stack

Summary

Jest 26.6.3 pulls jest-environment-jsdom@26 → jsdom@16 → deprecated:

• request@2.88.2
• request-promise-native@1.0.9
• har-validator@5.1.3

(We already have a narrow overrides.request.qs pin for security; that does not clear the deprecation warnings.)

Parent inventory: #445 (Cluster C).

Scope

• Upgrade jest, babel-jest, and related test tooling to a line that no longer depends on the deprecated request stack (Jest 28+ with modern jsdom, or at least a jsdom that dropped request).
• Update Jest config / snapshots if required by the major bump.
• Keep Node 18 CI (npm ci --legacy-peer-deps) green.

Acceptance criteria

• No request / request-promise-native / har-validator deprecation warnings on install from the Jest tree
• Full Jest suite passes
• Remove obsolete overrides.request only if nothing else still needs it

Related

• #445 Inventory of npm deprecation warnings

Start by running npm ci --legacy-peer-deps and inspecting the Jest dependency tree for request, request-promise-native, and har-validator. Review the Jest configuration and snapshots for changes required by the upgrade, then run the full Jest suite. Done means the deprecated warnings are gone, CI remains green, and the obsolete override is removed only if unused.