test(DashboardClient): add empty fallback coverage

[mayank200529]

Description

Fixes #2523

Added a new test file components/dashboard/DashboardClient.empty-fallback.test.tsx to verify empty and missing input fallback behavior for DashboardClient.

The test file includes 5 test cases covering:

• Empty languages array
• Empty activity array
• Empty insights array
• Empty achievements array
• Multiple empty dashboard collections together

All tests pass successfully.

Pillar

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

Visual Preview

No visual changes. This PR only adds test coverage.

Test result:

npm run test -- DashboardClient.empty-fallback.test.tsx

Test Files  1 passed (1)
Tests  5 passed (5)

Checklist before requesting a review:

• I have read the CONTRIBUTING.md file.
• I have tested these changes locally (npm run test -- DashboardClient.empty-fallback.test.tsx).
• 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 (not applicable, no SVG changes).
• (Recommended) I joined the CommitPulse Discord community for contributor discussions, mentorship, and faster PR support.

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