test(ControlsPanel-timezone-boundaries): verify Timezone Normalization & Calendar Data Boundary Alignment

[sheeeuWu]

Description

Adds ControlsPanel.timezone-boundaries.test.tsx with 5 tests covering the year dropdown's date logic: it shows the correct "current" year based on local time (not UTC), lists years with no gaps/duplicates, stays consistent across leap-year boundaries, and calls onYearChange with the right value on selection
Calendar-grid/locale-format steps from the original issue don't apply since ControlsPanel.tsx has no such logic of its own, it only renders a year picker

Fixes #6870

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).
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• 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.
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[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	3910.49 KB	3910.49 KB	0 B
Total CSS	326.92 KB	326.92 KB	0 B