Upgrade Vite 8, plugin-react 6, Vitest 4

Vite 6→8 (Rolldown/Oxc), @vitejs/plugin-react 4→6 (Babel-free), Vitest 3→4 (AST coverage)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

package.json

@@ -8,14 +8,14 @@
 	},
 	"devDependencies": {
 		"@biomejs/biome": "2.4.8",
-		"@vitest/coverage-v8": "^3.2.4",
+		"@vitest/coverage-v8": "^4.1.0",
 		"jscpd": "^4.0.8",
 		"knip": "^5.85.0",
 		"lefthook": "^1.11.0",
 		"oxlint": "^1.56.0",
 		"oxlint-tsgolint": "^0.17.1",
 		"typescript": "^5.8.0",
-		"vitest": "^3.0.0"
+		"vitest": "^4.1.0"
 	},
 	"scripts": {
 		"prepare": "lefthook install",