feat: migrate frontend React 18 → Svelte 5 + SvelteKit

Core logic portable (economy, balance, cosmetics, migrateSave) — zero rewrite.
136 tests green, identiques. Backend inchangé.

- Svelte 5 runes stores (game, auth, toast) remplacent Zustand
- SvelteKit adapter-static SPA (dist/ output, fallback index.html)
- Tailwind v4 conservé, design system .gp-* porté
- Transitions natives : slide, fly, scale, fade sur toute l'UI
- Sidebar tabbée (Production/Evolution/Collection) + CollapsiblePanel
- Mobile bottom sheet avec FAB toggle + backdrop blur
- Click particles réactifs Svelte (plus de DOM impératif)
- TadpoleSprite bounce + glow ring au clic
- Guide refait en accordéon, Achievements avec filtres
- a11y : focus-visible, Escape modals, aria-current, aria-labels
- CI/CD adapté (tests + build + rsync)
- Build 504K (vs ~1.2MB React)

Frontend/svelte.config.js

@@ -0,0 +1,28 @@
+import adapter from '@sveltejs/adapter-static';
+import { relative, sep } from 'node:path';
+
+/** @type {import('@sveltejs/kit').Config} */
+const config = {
+	compilerOptions: {
+		// defaults to rune mode for the project, execept for `node_modules`. Can be removed in svelte 6.
+		runes: ({ filename }) => {
+			const relativePath = relative(import.meta.dirname, filename);
+			const pathSegments = relativePath.toLowerCase().split(sep);
+			const isExternalLibrary = pathSegments.includes('node_modules');
+
+			return isExternalLibrary ? undefined : true;
+		}
+	},
+	kit: {
+		// adapter-auto only supports some environments, see https://svelte.dev/docs/kit/adapter-auto for a list.
+		// If your environment is not supported, or you settled on a specific environment, switch out the adapter.
+		// See https://svelte.dev/docs/kit/adapters for more information about adapters.
+		adapter: adapter({
+			fallback: 'index.html',
+			pages: 'dist',
+			assets: 'dist'
+		})
+	}
+};
+
+export default config;