feat: adopt Tailwind CSS utility classes for styling

[nicomiguelino]

Summary

• Rework index.html to use Tailwind utility classes instead of the custom CSS classes previously defined in src/css/style.css, keeping visual appearance and behavior unchanged (pure refactor, not a redesign).
• All classes referenced by JS/tests (.error-container, .error-message, .error-details, .error-key, .error-value) are preserved verbatim alongside the new Tailwind utility classes.
• The tr:last-child td { border-bottom: none } rule is reproduced via group on <tr> + group-last:border-b-0 on the <td>s (same technique used for position-based styling in the reference PRs).
• The #embed-container iframe { border: 0 } descendant rule (targeting the iframe injected at runtime by powerbi-client) is reproduced with the arbitrary variant [&_iframe]:border-0 on #embed-container.
• Slim src/css/style.css down to just the Tailwind layer/import setup (no app-specific CSS remains — the only custom styling was for the error screen, which used system font stacks already, so no @font-face needed to be preserved).
• Bump @screenly/edge-apps to ^1.3.0 for upcoming Tailwind CSS support.

This follows the same migration pattern applied in:

• feat: adopt Tailwind CSS utility classes for styling clock-app#12
• feat: adopt Tailwind CSS utility classes for styling weather-app#6

Test plan

• bun run type-check passes
• bun run build succeeds (tested against a local unpublished @screenly/edge-apps@1.3.0 tarball build with Tailwind support; the tarball install was fully reverted afterward — only the ^1.3.0 version bump in package.json is committed, and the lockfile is left untouched/stale until 1.3.0 is actually published, matching the reference PRs)
• Inspected the generated dist/css/style.css to confirm every arbitrary-value utility class used in index.html (colors, px values, border-b, group-last:, the [&_iframe]:border-0 variant, etc.) compiled to the expected CSS rules with correct values
• Visual screenshot verification: this repo has no Playwright/screenshot tooling (no @playwright/test dependency, no screenshots/ directory, no edge-apps-scripts screenshots wiring, unlike clock-app/weather-app), so step could not be completed. Visual correctness was instead verified by manually cross-checking the compiled CSS output against the original CSS rule-by-rule.