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/src/lib/components/ToastContainer.svelte

@@ -0,0 +1,36 @@
+<script lang="ts">
+	import { fly, scale } from 'svelte/transition';
+	import { backOut, quintOut } from 'svelte/easing';
+	import { getToasts } from '$lib/stores/toast.svelte';
+
+	const variantStyles: Record<string, { color: string; border: string; bg: string }> = {
+		success: { color: '#34d399', border: 'rgba(52,211,153,0.3)', bg: 'rgba(16,185,129,0.08)' },
+		info:    { color: '#60a5fa', border: 'rgba(96,165,250,0.3)', bg: 'rgba(59,130,246,0.08)' },
+		reward:  { color: '#fbbf24', border: 'rgba(251,191,36,0.3)', bg: 'rgba(245,158,11,0.08)' },
+		warning: { color: '#f87171', border: 'rgba(248,113,113,0.3)', bg: 'rgba(239,68,68,0.08)' },
+	};
+</script>
+
+{#if getToasts().length > 0}
+	<div class="fixed top-24 right-4 z-50 flex flex-col gap-2 pointer-events-none">
+		{#each getToasts() as t (t.id)}
+			{@const style = variantStyles[t.variant] || variantStyles.info}
+			<div
+				class="pointer-events-auto px-4 py-2.5 rounded-xl font-semibold text-sm shadow-2xl"
+				style="
+					background: rgba(17,17,17,0.9);
+					backdrop-filter: blur(12px);
+					border: 1px solid {style.border};
+					color: {style.color};
+					font-family: var(--font);
+					box-shadow: 0 0 20px {style.bg}, 0 8px 32px rgba(0,0,0,0.4);
+				"
+				in:fly={{ x: 80, duration: 350, easing: backOut }}
+				out:scale={{ duration: 200, start: 0.95, opacity: 0 }}
+				role="alert"
+			>
+				{t.message}
+			</div>
+		{/each}
+	</div>
+{/if}