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/ClickParticles.svelte

@@ -0,0 +1,50 @@
+<script lang="ts">
+	import { fly, fade } from 'svelte/transition';
+	import { quintOut } from 'svelte/easing';
+	import { formatNumber } from '$lib/utils/formatNumber';
+
+	interface Particle {
+		id: number;
+		x: number;
+		y: number;
+		gain: number;
+		isDouble: boolean;
+		isCrit: boolean;
+	}
+
+	let particles = $state<Particle[]>([]);
+	let nextId = 0;
+
+	export function spawn(x: number, y: number, gain: number, isDouble: boolean, isCrit: boolean) {
+		const id = nextId++;
+		// Random horizontal spread
+		const offsetX = (Math.random() - 0.5) * 40;
+		particles = [...particles, { id, x: x + offsetX, y, gain, isDouble, isCrit }];
+		setTimeout(() => {
+			particles = particles.filter(p => p.id !== id);
+		}, 1000);
+	}
+</script>
+
+<div class="fixed inset-0 pointer-events-none z-[100]">
+	{#each particles as p (p.id)}
+		{@const prefix = p.isCrit ? 'CRIT ' : p.isDouble ? 'x2 ' : ''}
+		{@const color = p.isCrit ? '#f59e0b' : p.isDouble ? '#a78bfa' : '#34d399'}
+		{@const size = p.isCrit ? '2rem' : p.isDouble ? '1.8rem' : '1.6rem'}
+		<span
+			class="absolute font-extrabold"
+			style="
+				left: {p.x}px;
+				top: {p.y}px;
+				color: {color};
+				font-size: {size};
+				font-family: var(--font);
+				text-shadow: 0 0 10px {color}60, 0 2px 6px rgba(0,0,0,0.7);
+			"
+			in:fly={{ y: 0, duration: 50 }}
+			out:fly={{ y: -90, duration: 900, easing: quintOut, opacity: 0 }}
+		>
+			{prefix}+{formatNumber(p.gain)}
+		</span>
+	{/each}
+</div>