Fail on ESLint warnings

Configure ESLint to fail on any number of warnings. This better surfaces
warnings on PR checks.

I considered putting this in the ESLint config file (.eslintrc.yaml),
however it cannot be configured there and there are no plans to support
that behavior¹.

¹ eslint/eslint#16804 (comment)

package.json

@@ -21,7 +21,7 @@
     "server": "npm run view",
     "build": "node auspice.js build --verbose",
     "prepare": "npm run build",
-    "lint": "eslint .",
+    "lint": "eslint --max-warnings=0 .",
     "lint:fix": "eslint --fix .",
     "type-check": "tsc",
     "type-check:watch": "npm run type-check -- --watch",