feat: adopt Tailwind CSS utility classes for styling

[nicomiguelino]

Summary

Part of the company-wide rollout converting edge-app repos to Tailwind CSS utility classes (see Screenly/clock-app#12 and Screenly/weather-app#6 for reference implementations).

• Rewrote index.html templates to use Tailwind utility classes (arbitrary-value bracket syntax) instead of custom CSS classes, reproducing every clamp() font-size, box-shadow, gradient, and text-shadow value exactly.
• Class names referenced by JS (querySelector/classList.add in src/main.ts and src/render.ts) are preserved verbatim: .severity-badge, .nws-content, .nws-preamble, .nws-forecast-list, .nws-wwwi-list, .wwwi-label, .wwwi-content, .period-label, .period-content.
• Deliberate deviation from the standard pattern: this app has no shared @screenly/edge-apps app-shell (no <auto-scaler>/<app-header>), so src/input.css keeps the bare @import 'tailwindcss'; (with Preflight enabled) rather than switching to the theme/base/utilities layered split + @screenly/edge-apps/styles import. Several plain elements here (<ul>, <li>, <h2>, <h3>, <p>) rely on Preflight's reset for zeroed margins/padding and list-style: none; dropping Preflight without extensive compensating classes would risk visual regressions (e.g. reappearing bullet points/list indentation) for no benefit, since there's no design-system CSS being layered in anyway.
• Status-banner color variants (status-banner-blue/red/orange/gray) and the "Actual" pulse animation (status-actual-pulse) are chosen dynamically at runtime via classList.add(...) based on the CAP alert's <status> value — these can't be expressed as static Tailwind utility classes on elements in index.html, so they're kept as plain CSS in src/input.css, unchanged.
• Deleted src/nws.css — its rules (list resets, bullet ::before content, label coloring) are now inlined directly as Tailwind utilities on the NWS forecast/WWWI list templates.
• Bumped @screenly/edge-apps to ^1.3.0 (unpublished; ships Tailwind support).
• Regenerated screenshots/* for all supported resolutions.

Test plan

• bun run type-check passes
• bun run build succeeds (pre-existing, unrelated Vite warnings about import.meta/screenly.js module type only)
• bun run screenshots (Playwright) regenerates all 10 resolution screenshots successfully
• Visually verified rendered screenshots at 1920x1080 (landscape) and 1080x1920 (portrait) — layout, spacing, and colors match pre-migration design
• Manually verified all four dynamic status-banner colors render correctly and pixel-identical to before, using temporarily-modified demo CAP data (not committed): blue (Exercise), red (Actual, including the pulse-animation class and stripe-pattern overlay), gray (Test), orange (Draft) — confirmed severity badge, keyword highlighting, and instruction-box styling all correct across severities
• Confirmed all JS-referenced class names (severity-badge, nws-*, period-*, wwwi-*) still present and functional after conversion