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/static/svg/cosmetics/armor-scales.svg

@@ -0,0 +1 @@
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 32 32"><g fill="#6b7280" opacity="0.5"><ellipse cx="13" cy="16" rx="3" ry="2"/><ellipse cx="19" cy="16" rx="3" ry="2"/><ellipse cx="16" cy="20" rx="3" ry="2"/><ellipse cx="13" cy="24" rx="3" ry="2"/><ellipse cx="19" cy="24" rx="3" ry="2"/></g></svg>

Frontend/static/svg/cosmetics/cap-swamp.svg

@@ -0,0 +1 @@
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 32 32"><ellipse cx="16" cy="8" rx="10" ry="4" fill="#34d399"/><rect x="6" y="7" width="20" height="3" rx="1" fill="#059669"/></svg>

Frontend/static/svg/cosmetics/cape-algae.svg

@@ -0,0 +1 @@
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 32 32"><path d="M10,14 Q6,20 8,28 L16,26 L24,28 Q26,20 22,14Z" fill="#059669" opacity="0.5"/></svg>

Frontend/static/svg/cosmetics/crown.svg

@@ -0,0 +1 @@
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 32 32"><polygon points="8,10 11,4 16,8 21,4 24,10" fill="#fbbf24"/><rect x="8" y="10" width="16" height="3" rx="1" fill="#f59e0b"/></svg>

Frontend/static/svg/cosmetics/flame-tail.svg

@@ -0,0 +1 @@
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 32 32"><path d="M14,22 Q12,18 16,16 Q20,18 18,22 Q20,20 18,26 Q16,28 14,26 Q12,24 14,22Z" fill="#f59e0b" opacity="0.8"/></svg>

Frontend/static/svg/cosmetics/glasses-savant.svg

@@ -0,0 +1 @@
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 32 32"><circle cx="11" cy="13" r="3" fill="none" stroke="#a78bfa" stroke-width="1.5"/><circle cx="21" cy="13" r="3" fill="none" stroke="#a78bfa" stroke-width="1.5"/><line x1="14" y1="13" x2="18" y2="13" stroke="#a78bfa" stroke-width="1"/></svg>

Frontend/static/svg/cosmetics/mask-frog.svg

@@ -0,0 +1 @@
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 32 32"><path d="M8,12 Q16,18 24,12 Q24,16 16,17 Q8,16 8,12Z" fill="#34d399" opacity="0.7"/></svg>

Frontend/static/svg/cosmetics/particles-gold.svg

@@ -0,0 +1 @@
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 32 32"><g fill="#fbbf24" opacity="0.6"><circle cx="6" cy="8" r="1.2"/><circle cx="26" cy="6" r="1"/><circle cx="4" cy="20" r="0.8"/><circle cx="28" cy="22" r="1.2"/><circle cx="10" cy="28" r="1"/><circle cx="22" cy="30" r="0.8"/><circle cx="16" cy="2" r="1"/><circle cx="2" cy="14" r="0.8"/><circle cx="30" cy="14" r="1"/></g></svg>

Frontend/static/svg/cosmetics/ribbon.svg

@@ -0,0 +1 @@
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 32 32"><path d="M12,22 L16,20 L20,22 L18,26 L16,24 L14,26Z" fill="#ec4899"/><circle cx="16" cy="21" r="2" fill="#f472b6"/></svg>