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/sitemap.xml

@@ -0,0 +1,23 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<urlset
+      xmlns="http://www.sitemaps.org/schemas/sitemap/0.9"
+      xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+      xsi:schemaLocation="http://www.sitemaps.org/schemas/sitemap/0.9
+            http://www.sitemaps.org/schemas/sitemap/0.9/sitemap.xsd">
+
+<url>
+  <loc>https://clickerz.tetardtek.com/</loc>
+  <lastmod>2026-03-20T12:00:00+00:00</lastmod>
+  <priority>1.00</priority>
+</url>
+<url>
+  <loc>https://clickerz.tetardtek.com/boutique</loc>
+  <lastmod>2026-03-20T12:00:00+00:00</lastmod>
+  <priority>0.80</priority>
+</url>
+<url>
+  <loc>https://clickerz.tetardtek.com/achievements</loc>
+  <lastmod>2026-03-20T12:00:00+00:00</lastmod>
+  <priority>0.80</priority>
+</url>
+</urlset>