test(success-guide): add massive scaling coverage for large markdown payloads

[Thacker-Meet]

Description

Fixes #4332

Added a dedicated massive-scaling test suite for app/components/SuccessGuide.tsx.

Coverage Added

• Verifies rendering of extremely large markdown payloads without truncation or failures.
• Confirms all guide steps remain visible and accessible when processing large content.
• Tests repeated render and unmount cycles to ensure component stability.
• Validates render performance under heavy mount/unmount workloads.
• Ensures dismiss functionality remains reliable under high interaction volume.

The test suite focuses on realistic scaling scenarios based on the actual responsibilities of the SuccessGuide component, validating large markdown handling, rendering stability, interaction reliability, and performance under heavy usage conditions.

Pillar

• 🛠️ Other (Bug fix, refactoring, docs)

Visual Preview

• N/A – Test-only changes.

Checklist before requesting a review:

• I have read the CONTRIBUTING.md file.
• I have tested these changes locally (localhost:3000/api/streak?user=YOUR_USERNAME).
• I have run npm run format and npm run lint locally and resolved all errors (CI will fail otherwise).
• My commits follow the Conventional Commits format (e.g., feat(themes): ..., fix(calculate): ...).
• I have started the repo.
• I have made sure that i have only one commit to merge in this PR.
• The SVG output matches the CommitPulse "premium quality" aesthetic standard (no raw elements, smooth animations, correct fonts).
• (Recommended) I joined the CommitPulse Discord community for contributor discussions, mentorship, and faster PR support.

[Aamod-Dev]

Thanks for the contribution. I went through the changes and the overall approach looks good.

[github-actions]

🎉 Congratulations @Thacker-Meet! Your PR has been successfully merged. 🚀

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