build: require Node 26 (engines, devEngines, @types/node)

Node 26 is the Active LTS and the fleet CI default (OpenLyceum/Baton#72).
Raise engines.node to >=26, bump @types/node to ^26, and add
devEngines.runtime with onFail: "error" so npm refuses to install or run
scripts on an older local Node.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01RTDmW22K4QUQA33XctdtDM

Author: veillette

package-lock.json

@@ -44,7 +44,7 @@
   "devDependencies": {
     "@biomejs/biome": "^2.6.2",
     "@playwright/test": "^1.64.1",
-    "@types/node": "^24.19.2",
+    "@types/node": "^26.6.6",
     "happy-dom": "^21.0.4",
     "png-to-ico": "^3.0.2",
     "sharp": "^0.35.5",
@@ -55,11 +55,18 @@
     "vitest": "^5.0.5"
   },
   "engines": {
-    "node": ">=24"
+    "node": ">=26"
   },
   "overrides": {
     "lodash": "~4.18.1",
     "three": "~0.125.2",
     "brace-expansion": "~5.0.12"
+  },
+  "devEngines": {
+    "runtime": {
+      "name": "node",
+      "version": ">=26",
+      "onFail": "error"
+    }
   }
 }