a11y(frontend): enhance accessibility support - Sprint 3 Story 5

Improve accessibility to meet WCAG 2.1 Level AA standards.

Changes: Added eslint-plugin-jsx-a11y, keyboard navigation, ARIA labels, SkipLink component, main-content landmark.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

eslint.config.mjs

@@ -1,10 +1,29 @@
 import { defineConfig, globalIgnores } from "eslint/config";
 import nextVitals from "eslint-config-next/core-web-vitals";
 import nextTs from "eslint-config-next/typescript";
+import jsxA11y from "eslint-plugin-jsx-a11y";
 
 const eslintConfig = defineConfig([
   ...nextVitals,
   ...nextTs,
+  {
+    rules: {
+      // Enable recommended jsx-a11y rules (plugin already included in nextVitals)
+      ...jsxA11y.configs.recommended.rules,
+      // Enforce stricter accessibility rules
+      "jsx-a11y/anchor-is-valid": "error",
+      "jsx-a11y/alt-text": "error",
+      "jsx-a11y/aria-props": "error",
+      "jsx-a11y/aria-proptypes": "error",
+      "jsx-a11y/aria-unsupported-elements": "error",
+      "jsx-a11y/role-has-required-aria-props": "error",
+      "jsx-a11y/role-supports-aria-props": "error",
+      "jsx-a11y/label-has-associated-control": "error",
+      "jsx-a11y/click-events-have-key-events": "warn",
+      "jsx-a11y/no-static-element-interactions": "warn",
+      "jsx-a11y/interactive-supports-focus": "warn",
+    },
+  },
   // Override default ignores of eslint-config-next.
   globalIgnores([
     // Default ignores of eslint-config-next: