ui: fix typo & add stylus style

[ILoveScratch2]

RT

修复了部分字符并添加样式（）

Summary by CodeRabbit

• Bug Fixes
  • Improved OAuth callback error message wording when bindings are missing or already assigned.
  • Refined Simplified Chinese locale strings, including corrected placeholder interpolation and help/validation text.
  • Fixed the “Flexible Duration” label spelling in contest rule settings.
• Style
  • Enhanced dark theme text/background styling for tab headers, problem tags, and search sorting.

[github-actions]

All contributors have signed the CLA ✍️ ✅
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[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro Plus

Run ID: 3c49a742-dea4-49ca-b07a-a903bd3c05a9

📥 Commits

Reviewing files that changed from the base of the PR and between 6e6afc2 and dd3436f.

📒 Files selected for processing (1)

• packages/hydrooj/locales/zh.yaml

💤 Files with no reviewable changes (1)

• packages/hydrooj/locales/zh.yaml

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Walkthrough

Corrects Simplified Chinese translations and placeholders, fixes OAuth and contest label wording, and adds dark-theme colors for section tabs, problem tags, and search sorting.

Estimated code review effort: 1 (Trivial) | ~5 minutes

Suggested reviewers: undefined-moe

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title is concise and accurately reflects the main changes: typo fixes and added Stylus styles in UI-related files.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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[ILoveScratch2]

I have read the CLA Document and I hereby sign the CLA