chore: fail lint on warnings

@eslint-react/eslint-plugin's recommended-typescript config sets 38 rules
at warn severity, where eslint-plugin-react's flat.recommended used error.
Several of those catch real defects rather than style, among them
web-api-no-leaked-timeout, web-api-no-leaked-event-listener,
set-state-in-effect and purity. ESLint's reportUnusedDisableDirectives
also defaults to warn.

Since `eslint .` exits 0 on warnings, all of the above could regress
without failing `npm test`. Add --max-warnings=0 to gate them.

format no longer shells out to the lint script, so that prettier --write
still runs when eslint --fix leaves an unfixable warning behind rather
than being short-circuited by the new gate.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

Author: tanem

package.json

@@ -22,8 +22,8 @@
     "clean:dist": "shx rm -rf dist",
     "clean:react": "node ./scripts/clean-react.js",
     "compile": "tsc -p tsconfig.base.json",
-    "format": "npm run lint -- --fix && prettier --write \"**/*.{js,ts,tsx}\"",
-    "lint": "eslint .",
+    "format": "eslint . --fix && prettier --write \"**/*.{js,ts,tsx}\"",
+    "lint": "eslint . --max-warnings=0",
     "postbundle": "npm run clean:compiled && shx cp ./index.js ./dist/index.js",
     "prepare": "npm run build",
     "release": "tanem-scripts release",