chore(frontend): Tailwind v4 CSS-first config

Move every tailwind.config.js option into src/style.css: @import,
@plugin flowbite/plugin, @source for the flowbite-svelte dist
(node_modules is gitignored so auto-detection skips the lib),
@theme for the custom primary scale, and @utility container
porting the old center plus responsive padding and max-width
ladders. darkMode media is v4s default so it needs no equivalent.
vite.config.ts gains the tailwindcss() plugin; index.html loses the
dead flowbite.js tag.

style.css also carries two v4-behavior restorations found while
verifying the built CSS: pointer cursor on buttons (v4 preflight
dropped v3s rule) and the container max-width ladder the first
pass at this file omitted.

frontend/vite.config.ts

@@ -1,5 +1,6 @@
 import {defineConfig} from 'vite'
 import {svelte} from '@sveltejs/vite-plugin-svelte'
+import tailwindcss from '@tailwindcss/vite'
 import wails from '@wailsio/runtime/plugins/vite'
 
 // https://vitejs.dev/config/
@@ -9,5 +10,5 @@ export default defineConfig({
     port: Number(process.env.WAILS_VITE_PORT) || 5173,
     strictPort: true,
   },
-  plugins: [svelte(), wails('./bindings')]
+  plugins: [tailwindcss(), svelte(), wails('./bindings')]
 })