perf(assets): convert images to webp and check asset paths

Convert 26 PNG/JPG assets to WebP: max 1600 px, q80, diagrams lossless.
src/assets shrinks from 8.3 MB to 4.2 MB.
Use me.jpg for og:image and twitter:image; some crawlers skip WebP.
Add scripts/check-assets.mjs to lint, so a wrong asset path fails lint,
not only at runtime.

package.json

@@ -7,8 +7,9 @@
     "build": "ng build",
     "watch": "ng build --watch --configuration development",
     "test": "ng test --watch=false",
-    "lint": "ng lint",
-    "i18n:check": "node scripts/check-i18n.mjs"
+    "lint": "ng lint && npm run assets:check",
+    "i18n:check": "node scripts/check-i18n.mjs",
+    "assets:check": "node scripts/check-assets.mjs"
   },
   "private": true,
   "dependencies": {