test(not-found): add massive scaling coverage for repeated renders and layout stability

[Thacker-Meet]

Description

Fixes #4360

Added a dedicated massive-scaling test suite for the app/not-found.tsx page.

What was tested?

• Repeated component mounts to verify rendering stability.
• Terminal content integrity across multiple render cycles.
• Navigation link availability under high render volume.
• Render performance remains within acceptable limits.
• Layout structure preservation during bulk rendering scenarios.

The tests focus on validating component behavior under high-volume rendering conditions while ensuring UI structure and accessibility remain intact.

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.

[Thacker-Meet]

Hi @Aamod007 @souravjhahind

I am a GSSoC'26 contributor.

please can you add the labels "GSSoC 2026" and "GSSoC:approved".

[Thacker-Meet]

hi @Aamod007

please can you add another GSSoC label "GSSoC:aprroved", if this label is not present in the Pull Request and GSSoC'26 will not count this PR.

[github-actions]

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