fix(deps): re-pin toolchain after auto-merge regressions

dependabot auto-merge landed eslint@^10 + @tsparticles@^4 (d13b984 pins
ignored, no branch protection). Restore known-good stack: eslint ^9, TS ^6,
tsparticles ^3. Full gate green.

package.json

@@ -34,9 +34,9 @@
     "@tabler/icons-react": "^3.47.0",
     "@tanstack/react-query": "^5.103.1",
     "@tanstack/react-table": "^9.2.4",
-    "@tsparticles/engine": "^4",
+    "@tsparticles/engine": "^3",
     "@tsparticles/react": "^3",
-    "@tsparticles/slim": "^4",
+    "@tsparticles/slim": "^3",
     "better-auth": "^1.7.5",
     "class-variance-authority": "^0.7.1",
     "clsx": "^2.1.1",
@@ -81,7 +81,7 @@
     "@types/react": "^19",
     "@types/react-dom": "^19",
     "@vitest/coverage-v8": "^5.0.1",
-    "eslint": "^10",
+    "eslint": "^9",
     "eslint-config-next": "16.3.5",
     "eslint-plugin-react": "^7.37.5",
     "husky": "^9.1.7",