chore: add JS/ESLint toolchain, refactor onclick to event delegation

- Add ESLint config for web/ui (flat config, golangci-lint-compatible)
- Add js-lint task to mise.toml (npm run lint in web/ui)
- Add ESLint check to check-toolchain.sh
- Add .golangci.yml for golangci-lint v2 with correct exclusions
- Refactor app.js: replace inline onclick with data-action + event delegation
- Add null checks and HTTP status checks to browseWavs
- Add web/ui/node_modules/ to .gitignore

web/ui/eslint.config.js

@@ -0,0 +1,45 @@
+const globals = require('globals');
+
+module.exports = [
+  {
+    files: ['**/*.js'],
+    languageOptions: {
+      ecmaVersion: 2022,
+      sourceType: 'script',
+      globals: {
+        ...globals.browser,
+        AudioContext: 'readonly',
+        requestAnimationFrame: 'readonly',
+        cancelAnimationFrame: 'readonly',
+        fetch: 'readonly',
+        EventSource: 'readonly',
+        document: 'readonly',
+        console: 'readonly',
+        setTimeout: 'readonly',
+        Math: 'readonly',
+        JSON: 'readonly',
+        location: 'readonly',
+        encodeURIComponent: 'readonly',
+        decodeURIComponent: 'readonly',
+        parseInt: 'readonly',
+        Number: 'readonly',
+        Promise: 'readonly',
+        Object: 'readonly',
+        Array: 'readonly',
+        Map: 'readonly',
+        process: 'readonly',
+        __dirname: 'readonly',
+        require: 'readonly',
+        module: 'readonly',
+        exports: 'readonly'
+      }
+    },
+    rules: {
+      "no-unused-vars": ["warn", { "argsIgnorePattern": "^_", "varsIgnorePattern": "^_" }],
+      "no-redeclare": "warn",
+      "no-unreachable": "warn",
+      "eqeqeq": ["error", "always"],
+      "prefer-const": "warn"
+    }
+  }
+];