refactor(reports): dedupe claim-error-code parsing into parseJsonResponse

[pedrofrxncx]

Small reduction in apps/api/src/tools/reports/auth-client.ts: parseClaimErrorCode hand-rolled its own "read text, tolerate empty, JSON.parse, tolerate parse failure" logic — the exact same tolerant-parse shape parseJsonResponse already implements two functions below it (and is already used by every other response handler in this file, e.g. fetchCommerceDiscoveryAuth's token check, bindCommerceDiscoveryResource, fetchCommerceDiscoveryConnectionStatus).

Why a maintainer wants it: one tolerant-parse implementation instead of two copies drifting apart — a future robustness fix (e.g. a body-size cap) only needs to land once.

Behavior preserved for every input:

• Empty/unparsable body -> parseJsonResponse returns undefined -> parsed?.error is undefined -> isClaimCode(undefined) is false -> "unknown" (same as before).
• Parsed JSON with a recognized error code -> unchanged.
• Parsed JSON with an unrecognized error (or missing error) -> "unknown" (same as before).

-9 / +5 lines, no behavior change, no new exports.

How I verified: bun test apps/api/src/tools/reports/auth-client.test.ts (26 pass, including the 403/409/400/non-JSON-body claim-error tests that exercise this exact function), bunx tsc --noEmit in apps/api, bunx oxlint on the touched file, bun run fmt. Full CI validates the rest.

Reviewer check: bun test apps/api/src/tools/reports/auth-client.test.ts

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Summary by cubic

Deduplicates claim-error parsing in the reports auth client by routing parseClaimErrorCode through parseJsonResponse. This removes duplicate tolerant JSON parsing and preserves behavior for all responses.

Review notes

• parseClaimErrorCode now uses parseJsonResponse; empty or non-JSON bodies still return "unknown".
• Recognized error codes behave the same; unrecognized or missing values still return "unknown".
• No API or export changes; only apps/api/src/tools/reports/auth-client.ts is modified. Run bun test apps/api/src/tools/reports/auth-client.test.ts to verify the claim-error cases.

^{Written for commit 04ebd74. Summary will update on new commits.}