fix(identity): reduce noisy client-error logs

[raymondjacobson]

Summary

• Move expected identity-service 4xx responses from error logs to debug logs while preserving 5xx responses at error level.
• Redact sensitive query parameters in request log context and add compact error shaping for axios-style failures.
• Use the compact error shape for auth backfill failures so dependency errors do not serialize giant request objects.
• Add helper tests covering 4xx/5xx log levels, query redaction, and compact axios-style error fields.

Context

A live stern -n identity-service . sample showed most app-container log volume coming from expected client-side 400s (/users/check?email= and invalid /authentication credentials). The pasted updateBlockchainIds giant log and repeated download-app email delivery logs come from the older deployed notification runtime; current code has already removed that runtime, and this PR handles the remaining central response/logging path.

Verification

• node -c packages/identity-service/src/apiHelpers.js && node -c packages/identity-service/src/authMiddleware.js && node -c packages/identity-service/src/logging.js && node -c packages/identity-service/test/apiHelpersTest.js && node -c packages/identity-service/test/index.ts
• git diff --check

Not run: full npm test -w identity-service; this worktree is missing local workspace test dependencies (../../node_modules/ts-mocha, plus bunyan/mocha). The attempted run created the standard test Postgres/Redis containers before failing, and those containers were removed.

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