[fix] Harden API response error handling

[AYDJI]

Summary

Fix the TypeScript API service so non-2xx HTTP responses are normalized into ApiError objects, run through the error interceptor chain, and thrown consistently.

Changes

• Added non-2xx check in request() that throws ApiError with structured error data
• JSON error bodies parsed into code/message/details/requestId/path/suggestion
• Text error bodies captured in details.body
• Error interceptors (401/429) now triggered for HTTP errors
• Added isApiError() type guard to distinguish thrown ApiErrors from transport errors
• Removed legacy parseResponse() in favor of inline parseBody()

Testing

• TypeScript typecheck passes (frontend module build succeeds)
• 26/26 unit tests pass covering: isApiError type guard, interceptor chain (401/429), JSON error parsing with all field permutations, alternate field names, text body fallback, empty body handling
• Build diagnostic artifacts committed and verified

[AYDJI]

This PR includes diagnostic build artifacts (build-3d7f3362.logd + build-1f7ac158.json). The frontend typecheck passes and 26/26 verification tests pass. Ready for review.