Revert PR #62: tailwindcss 3.4.19 → 4.3.0 (breaks production build)

[nx-thaddeusaid]

Summary

Reverts #62 (build(deps-dev): bump tailwindcss from 3.4.19 to 4.3.0). The bump broke the production Docker build:

[plugin vite:css] /app/RogueTechWarMap/src/index.css:undefined:NaN
Error: [postcss] It looks like you're trying to use `tailwindcss` directly as a PostCSS plugin.
The PostCSS plugin has moved to a separate package, so to continue using Tailwind CSS with PostCSS
you'll need to install `@tailwindcss/postcss` and update your PostCSS configuration.

Tailwind v4 is a major release that moved its PostCSS plugin to @tailwindcss/postcss, but the dependabot PR only updated package.json — it did not add the new package or update postcss.config.js, so every production build since the merge has failed.

Reverting to ^3.4.12 restores the last known-good state. A proper v4 migration (separate PR) would need to:

• Add @tailwindcss/postcss to devDependencies
• Update postcss.config.js to use @tailwindcss/postcss instead of tailwindcss
• Verify @tailwind base/components/utilities directives in src/index.css (v4 prefers @import "tailwindcss")

Test plan

• yarn install --frozen-lockfile succeeds
• VITE_BASE_URL=/warmap yarn build succeeds (built in 549ms, 2127 modules)
• CI passes on this PR