Add unit tests for the previously-untested proxy handlers (auth/mfa/verify,
auth/oauth/[provider], telemetry/ingest) covering success, error-status
forwarding, default error messages, validation, and the 502 unreachable path.
Add tracker-client tests asserting every endpoint path/method/body contract
and x-product-id header injection, plus product-config request resolution.
Overall coverage rises from ~90% to 94% stmts / 87% branch / 94% funcs. Also
fix the vitest coverage thresholds: the legacy global nesting was silently
ignored by the v8 provider, so the 80% gate was never enforced.
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Co-Authored-By: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>
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