fix: localize warning messages

[maxchang3]

🔗 Linked issue

resolves #2049

🧭 Context

Some warnings shown in the skills modal and diff sidebar were previously hardcoded English strings produced on the server.

This change localizes those warnings by returning structured warning messages with translation keys, then translating them in the UI through a shared composable.

📚 Description

Changes:

• introduce a shared WarningMessage type for structured warnings
• Update server-side warning generation to return translation keys instead of raw strings
• add corresponding i18n entries and schema updates
• translate warnings in the UI via useI18nWarning()
• update related tests

I went back and forth a bit on whether these warnings should remain entirely client-derived, since there are already places in the project where warning-like UI text is built on the frontend.

Following the discussion in #2049 with @ShroXd, it felt worthwhile to establish this pattern here: it not only improves i18n handling, but also gives us a clearer structure for information flow, while translation keys remain semantic and readable.

So this PR also serves as an experiment to explore what this direction would look like in practice.

---

One thing to note is that this also introduces a dynamic key mechanism that isn't currently accepted by the existing i18n validation.

❌ Unused keys: 3
  ./i18n/locales/en.json
    package.skills.warnings.no_license
    package.skills.warnings.no_compatibility
    compare.warnings.files_truncated

❌ Build failed: missing, unused or dynamic keys detected

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Project	Deployment	Actions	Updated (UTC)
npmx.dev	Ready	Preview, Comment	Mar 18, 2026 5:04pm

2 Skipped Deployments

Project	Deployment	Actions	Updated (UTC)
docs.npmx.dev	Ignored		Mar 18, 2026 5:04pm
npmx-lunaria	Ignored		Mar 18, 2026 5:04pm

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Tracked Files

File	Note
i18n/locales/en.json	Source changed, localizations will be marked as outdated.
i18n/locales/zh-CN.json	Localization changed, will be marked as complete.

Warnings reference

Icon	Description
🔄️	The source for this localization has been updated since the creation of this pull request, make sure all changes in the source have been applied.

[codecov]

Codecov Report

❌ Patch coverage is 66.66667% with 2 lines in your changes missing coverage. Please review.
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
app/components/Package/SkillsModal.vue	0.00%	1 Missing and 1 partial ⚠️

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