Replace Tailwind CDN with a local build process

[Copilot]

index.html loaded Tailwind via https://cdn.tailwindcss.com (the play CDN, not intended for production) and used the CDN-only <style type="text/tailwindcss"> block for custom CSS. This replaces that with a proper offline build that ships only the CSS classes actually used.

Changes

• package.json + tailwind.config.js — Adds tailwindcss@^3.4.19 with a build script (tailwindcss -i src/input.css -o src/tailwind.css --minify); content scanning covers src/**/*.html and src/**/*.js

• src/input.css — New CSS source file consolidating the Tailwind directives and the two inline style blocks extracted from index.html:

  @tailwind base;
  @tailwind components;
  @tailwind utilities;
  
  :root {
    --wake-on: theme(colors.emerald.600);
    --wake-off: theme(colors.red.600);
  }
  
  .wake-on { transition: color 0.3s ease-in-out; color: var(--wake-on); }
  .wake-off { transition: color 0.3s ease-in-out; color: var(--wake-off); }

• src/index.html — Removes the CDN <script> and both <style> blocks; adds <link rel="stylesheet" href="tailwind.css">

• Dockerfile — Multi-stage build: Node Alpine stage runs npm ci && npm run build to emit src/tailwind.css, BusyBox stage copies the finished src/ directory

• .gitignore — Excludes node_modules/ and the generated src/tailwind.css

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