feat(eslint): add jsx-a11y accessibility rules as warnings

Install eslint-plugin-jsx-a11y and add 24 recommended rules to the
nextjs ESLint config, all set to warn. Baseline: 292 warnings
(207 label-has-associated-control, 52 no-static-element-interactions,
22 click-events-have-key-events, 10 no-autofocus, 1 html-has-lang).

Will be upgraded to errors after Phase 5c fixes core components.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

tooling/eslint/package.json

@@ -18,5 +18,8 @@
   "peerDependencies": {
     "eslint": "^9.0.0",
     "typescript": "^5.0.0"
+  },
+  "devDependencies": {
+    "eslint-plugin-jsx-a11y": "^6.10.2"
   }
 }

tooling/eslint/src/nextjs.js

@@ -1,5 +1,6 @@
 import baseConfig from "./base.js";
 import reactHooks from "eslint-plugin-react-hooks";
+import jsxA11y from "eslint-plugin-jsx-a11y";
 
 /** @type {import("eslint").Linter.FlatConfig[]} */
 export default [
@@ -7,6 +8,7 @@ export default [
   {
     plugins: {
       "react-hooks": reactHooks,
+      "jsx-a11y": jsxA11y,
     },
     rules: {
       "react-hooks/rules-of-hooks": "error",
@@ -15,6 +17,31 @@ export default [
         "error",
         { checksVoidReturn: { attributes: false } },
       ],
+      // Accessibility: start as warn, upgrade to error after fixes
+      "jsx-a11y/alt-text": "warn",
+      "jsx-a11y/anchor-has-content": "warn",
+      "jsx-a11y/anchor-is-valid": "warn",
+      "jsx-a11y/aria-props": "warn",
+      "jsx-a11y/aria-proptypes": "warn",
+      "jsx-a11y/aria-role": "warn",
+      "jsx-a11y/aria-unsupported-elements": "warn",
+      "jsx-a11y/click-events-have-key-events": "warn",
+      "jsx-a11y/heading-has-content": "warn",
+      "jsx-a11y/html-has-lang": "warn",
+      "jsx-a11y/img-redundant-alt": "warn",
+      "jsx-a11y/interactive-supports-focus": "warn",
+      "jsx-a11y/label-has-associated-control": "warn",
+      "jsx-a11y/no-access-key": "warn",
+      "jsx-a11y/no-autofocus": "warn",
+      "jsx-a11y/no-distracting-elements": "warn",
+      "jsx-a11y/no-noninteractive-element-interactions": "warn",
+      "jsx-a11y/no-noninteractive-tabindex": "warn",
+      "jsx-a11y/no-redundant-roles": "warn",
+      "jsx-a11y/no-static-element-interactions": "warn",
+      "jsx-a11y/role-has-required-aria-props": "warn",
+      "jsx-a11y/role-supports-aria-props": "warn",
+      "jsx-a11y/scope": "warn",
+      "jsx-a11y/tabindex-no-positive": "warn",
     },
   },
 ];