FIX: Year selection in the customization studio (JhaSourav07#648)

## Description
This PR fixes a dark mode styling issue where the selected value in the
Year dropdown becomes unreadable due to insufficient text/background
contrast.

The dropdown now correctly applies dark theme styles so the selected
year remains visible and accessible in dark mode.

Fixes JhaSourav07#646 

## Pillar

- [x] 🎨 Pillar 1 — New Theme Design
- [x] 🛠️ Other (Bug fix, refactoring, docs)

## Visual Preview

## BEFORE 

<img width="667" height="550" alt="Screenshot 2026-05-27 202142"
src="https://github.com/user-attachments/assets/ea8fdffe-1d82-4a1d-af61-98095421aaa4"
/>

##  AFTER

<img width="631" height="392" alt="image"
src="https://github.com/user-attachments/assets/70823614-375f-4ecc-9dbf-20afeca63a46"
/>


## Checklist before requesting a review:

- [x] I have read the `CONTRIBUTING.md` file.
- [x] I have tested these changes locally
(`localhost:3000/api/streak?user=YOUR_USERNAME`).
- [x] I have run `npm run format` and `npm run lint` locally and
resolved all errors (CI will fail otherwise).
- [x] My commits follow the Conventional Commits format (e.g.,
`feat(themes): ...`, `fix(calculate): ...`).
- [x] I have started the repo.
- [x] I have made sure that i have only one commit to merge in this PR.
- [x] The SVG output matches the CommitPulse "premium quality" aesthetic
standard (no raw elements, smooth animations, correct fonts).
- [x] (Recommended) I joined the CommitPulse Discord community for
contributor discussions, mentorship, and faster PR support.

Author: JhaSourav07