test: add error handler coverage (#1266)

[mittalsonal]

Description\n- add focused Vitest coverage for logError in development mode\n- verify production mode serializes context without exposing stack traces\n- keep the change scoped to a new est/error-handler.test.ts file only\n\n## Related Issue\n- Closes #1266\n\n## Checklist\n- [x] test-only change\n- [x] git diff --check passes\n- [x] follows existing Vitest style in the repo\n\n## Pillar\n- Open Source\n

[vercel]

@mittalsonal is attempting to deploy a commit to the PRIYANSHU DOSHI's projects Team on Vercel.

A member of the Team first needs to authorize it.

[mittalsonal]

Kind request for GSSoC labels when reviewed: gssoc:approved, one level:* label, and ype:testing if it fits the repo’s scoring rubric. Thanks!

[mittalsonal]

Verification completed locally:

• git diff --check

Attempted:

• npx vitest run test/error-handler.test.ts

The targeted Vitest run is currently blocked in this workspace because the repo's local test dependencies are not installed, so vitest.config.ts could not resolve vitest/config here. The change itself is test-only and stays within the repo's existing Vitest pattern.

[github-actions]

GSSoC Label Checklist 🏷️

@Priyanshu-byte-coder — please apply the appropriate labels before merging:

Difficulty (pick one):

• level:beginner — 20 pts
• level:intermediate — 35 pts
• level:advanced — 55 pts
• level:critical — 80 pts

Quality (optional):

• quality:clean — ×1.2 multiplier
• quality:exceptional — ×1.5 multiplier

Validation (required to score):

• gssoc:approved — counts for points
• gssoc:invalid / gssoc:spam / gssoc:ai-slop — does not score

Type labels (type:*) are auto-detected from files and title. Review and adjust if needed.
Points formula: (difficulty × quality_multiplier) + type_bonus