feat: toast system — feedback visuel global (react-hot-toast)

- Toaster dark theme (bottom-right, 3s/4s)
- Combat: erreur cooldown/endurance en toast
- Craft: toast start + collect + erreurs
- Forge: toast succès/échec + erreurs
- Shop: toast achat + erreurs
- Inventaire: toast vente + erreurs
- Fix forge costs frontend (200/400/700)

frontend/package-lock.json

@@ -12,6 +12,7 @@
         "lucide-react": "^0.577.0",
         "react": "^19.2.4",
         "react-dom": "^19.2.4",
+        "react-hot-toast": "^2.6.0",
         "react-router-dom": "^7.13.1"
       },
       "devDependencies": {
@@ -1545,7 +1546,6 @@
       "version": "3.2.3",
       "resolved": "https://registry.npmjs.org/csstype/-/csstype-3.2.3.tgz",
       "integrity": "sha512-z1HGKcYy2xA8AGQfwrn0PAy+PB7X/GSj3UVJW9qKyn43xWa+gl5nXmU4qqLMRzWVLFC8KusUX8T/0kCiOYpAIQ==",
-      "dev": true,
       "license": "MIT"
     },
     "node_modules/debug": {
@@ -1952,6 +1952,15 @@
         "url": "https://github.com/sponsors/sindresorhus"
       }
     },
+    "node_modules/goober": {
+      "version": "2.1.18",
+      "resolved": "https://registry.npmjs.org/goober/-/goober-2.1.18.tgz",
+      "integrity": "sha512-2vFqsaDVIT9Gz7N6kAL++pLpp41l3PfDuusHcjnGLfR6+huZkl6ziX+zgVC3ZxpqWhzH6pyDdGrCeDhMIvwaxw==",
+      "license": "MIT",
+      "peerDependencies": {
+        "csstype": "^3.0.10"
+      }
+    },
     "node_modules/has-flag": {
       "version": "4.0.0",
       "resolved": "https://registry.npmjs.org/has-flag/-/has-flag-4.0.0.tgz",
@@ -2673,6 +2682,23 @@
         "react": "^19.2.4"
       }
     },
+    "node_modules/react-hot-toast": {
+      "version": "2.6.0",
+      "resolved": "https://registry.npmjs.org/react-hot-toast/-/react-hot-toast-2.6.0.tgz",
+      "integrity": "sha512-bH+2EBMZ4sdyou/DPrfgIouFpcRLCJ+HoCA32UoAYHn6T3Ur5yfcDCeSr5mwldl6pFOsiocmrXMuoCJ1vV8bWg==",
+      "license": "MIT",
+      "dependencies": {
+        "csstype": "^3.1.3",
+        "goober": "^2.1.16"
+      },
+      "engines": {
+        "node": ">=10"
+      },
+      "peerDependencies": {
+        "react": ">=16",
+        "react-dom": ">=16"
+      }
+    },
     "node_modules/react-router": {
       "version": "7.13.1",
       "resolved": "https://registry.npmjs.org/react-router/-/react-router-7.13.1.tgz",