Upgrade to Tailwind CSS v4

[Copilot]

• Research Tailwind CSS v4 migration requirements
• Run automatic upgrade tool to update input.css
• Install @tailwindcss/cli package
• Update build scripts (no changes needed - CLI binary name remains the same)
• Remove tailwind.config.js (v4 uses CSS-based config with auto content detection)
• Test the build process (successful)
• Run linting and tests (passing except pre-existing test failure)
• Code review (no issues found)
• Security scanning (no issues found)
• Update pnpm-lock.yaml for new dependency
• Final verification (complete)

Summary

Successfully upgraded Tailwind CSS from v3.4.17 to v4.1.18:

Key Changes

• Updated src/input.css to use @import 'tailwindcss' (v4 syntax)
• Added @tailwindcss/cli package for v4 CLI support
• Removed tailwind.config.js (v4 uses automatic content detection)
• Updated pnpm-lock.yaml to include new dependency
• Generated CSS is smaller and uses modern CSS features

Testing

• ✅ Build process: successful
• ✅ Linter: passing (1 pre-existing warning)
• ✅ TypeScript: passing
• ✅ Tests: 157 passing (1 pre-existing test failure unrelated to Tailwind)
• ✅ Code review: no issues
• ✅ Security scan: no issues
• ✅ CI: lockfile updated, should now pass

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[hogashi]

@copilot failing CI

[Copilot]

@copilot failing CI

Fixed the CI failure by updating pnpm-lock.yaml to include the new @tailwindcss/cli dependency. The lockfile was out of sync with package.json, causing the frozen-lockfile check to fail.

Commit: a9a9b69