Add tests for the ThemeContext system-preference change listener

[1nonlypiece]

📌 Description

src/context/ThemeContext.tsx subscribes to
matchMedia('(prefers-color-scheme: dark)') and only auto-switches when the
user has not stored an explicit theme. The existing theme tests (per the title
list) cover persistence and attribute sync, but the OS-preference change
listener and its "respect manual override" guard are easy to regress and
deserve direct coverage.

This issue adds tests for the media-query listener.

🎯 Requirements and Context

• Mock matchMedia with a controllable change dispatcher.
• With no stored theme, assert a system change to dark updates the theme.
• With a stored theme, assert a system change is ignored.
• Assert the listener is removed on unmount (no leak / no late updates).

🛠️ Suggested Execution

1. Fork the repo and create a branch

git checkout -b test/theme-context-system-listener

2. Implement changes

• Add src/context/__tests__/ThemeContext.systemListener.test.tsx (or extend
  the existing theme test).
• Provide a matchMedia mock exposing addEventListener/removeEventListener.

3. Test and commit

• Run: npm run test
• Edge cases: stored vs unstored theme, unmount before change, repeated changes.

Example commit message

test: cover ThemeContext system-preference change listener

✅ Guidelines

• Minimum 95% test coverage on the touched lines.
• No regressions in theme auto-switching.
• Keep the diff small and reviewer-friendly.
• Timeframe: 96 hours.

🏷️ Labels

type-testing · area-frontend · MAYBE REWARDED · GRANTFOX OSS · OFFICIAL CAMPAIGN

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[DevALVIN-24]

@DevALVIN-24 has applied to work on this issue as part of the Stellar Wave Program's 6th wave.

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[femiolutayo]

@femiolutayo has applied to work on this issue as part of the Stellar Wave Program's 6th wave.

Hello Maintainer. I would love to resolve this issue in no time. Please assign to me. Thank you.

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[Truphile]

@Truphile has applied to work on this issue as part of the Stellar Wave Program's 6th wave.

​Hi team, I'd like to apply for this task.
​As a returning contributor, I have a strong understanding of how this component integrates into our wider system architecture. Because I’ve executed identical production requirements in past systems, I’m well-prepared to handle this cleanly—ensuring strict validation rules, comprehensive test coverage for edge cases, and zero regressions on existing flows.
​Ready to pick this up and dive straight into the branch upon assignment.

ℹ️ Repo Maintainers: To accept this application, review their application or assign @Truphile to this issue.

[drips-wave]

Congratulations, @Truphile! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on June 30, 2026.

🧑‍💻 @Truphile: Please resolve the issue such that the repo's maintainers have enough time to review your contribution before the due date. You'll earn Points for completing the issue on-time, which will make you eligible for a share of the Stellar Wave Program's reward pool.

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