test: add TypeScript compiler validation coverage

[SreeyaKumari]

Description

Fixes #2802

Pillar

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

Visual Preview

##Changes

• Added type compiler validation tests for ComparePage
• Added expectTypeOf assertions for interface properties
• Added optional field validation coverage
• Added CompareResponse structure validation
• Verified schema/type constraints remain stable

##Validation
-vitest run passes

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.

[vercel]

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[github-actions]

👋 Hey @SreeyaKumari, welcome to CommitPulse! 🎉

Thanks for opening your first pull request — this is a big deal and we appreciate the effort!

While you wait for a review, please double-check:

• ✅ You've read the CONTRIBUTING.md checklist
• ✅ npm run lint, npm run format, and npm run test all pass locally
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[github-actions]

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