fix: normalize non-2xx HTTP responses into ApiError objects

[dev-khimesh]

Summary

Harden API response error handling: non-OK HTTP responses are now normalized into ApiError objects, run through the existing error interceptor chain, and thrown consistently.

Changes

Before

request<T>() returned every HTTP response as a successful ApiResponse<T>, even 4xx/5xx responses. Callers had to duplicate status checks, and the error interceptor chain (401, 429 handlers) was never exercised for HTTP errors.

After

• ✅ request<T>() checks response.ok — non-2xx responses are parsed into ApiError and thrown
• ✅ Structured JSON error bodies (with message, error, details, suggestion fields) are safely extracted
• ✅ Text error bodies fall back gracefully
• ✅ Error interceptors run for HTTP errors — 401 triggers auth refresh, 429 triggers rate-limit backoff
• ✅ Request ID and path are preserved in the error object
• ✅ Status-based suggestions guide users (401 → login, 429 → wait, 500 → try later)
• ✅ Timeout and network errors continue to use existing normalizeError handling
• ✅ Retry logic correctly skips non-2xx HTTP errors (not status codes) while preserving timeout retries
• ✅ Existing 2xx success path is unchanged

Required Validation

Closes #1