test: add timezone boundaries tests for PreviewPanel

[deepsikha-dash]

Description

Fixes #6920

Pillar

• 🎨 Pillar 1 — New Theme Design
• 📐 Pillar 2 — Geometric SVG Improvement
• 🕐 Pillar 3 — Timezone Logic Optimization
• 🛠️ Other (Bug fix, refactoring, docs)

Visual Preview

N/A

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 updated README.md if I added a new theme or URL parameter.
• 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.

[github-actions]

📦 Next.js Bundle Size Report (Gzipped Sizes)

✨ No significant bundle size changes detected.

📊 Summary of Totals

Category	PR Size	Base Size	Difference
Total JS	3917.41 KB	3917.41 KB	0 B
Total CSS	325.86 KB	325.86 KB	0 B

[Aamod007]

Hello! Thanks for adding the timezone boundaries tests for the \PreviewPanel. Validating component behavior across different time zones ensures our user previews are consistent globally. The tests look perfect and all CI checks are green!

Labels assigned:

• \level:beginner: Standard timezone bounds testing.
• \quality:clean: Clear and focused test cases.
• \ ype:testing: Purely adds test coverage.