chore(deps): upgrade ESLint 8 → 10 (flat config) and chai 4 → 6 (#1934)

* chore(deps): upgrade ESLint 8 → 10 (flat config) and chai 4 → 6

Migrate ESLint to flat config format (eslint.config.mjs), remove
.eslintrc. Upgrade chai to v6 which includes built-in TypeScript
types, remove @types/chai.

- Replace eslint-plugin-import with eslint-plugin-import-x (ESLint 10 compatible fork)
- Add typescript-eslint unified package for flat config support
- Disable import-x/no-unused-modules (incompatible with ESLint 10)
- Add test file overrides for chai expressions and sinon namespace
- Remove --ext flag from eslint scripts (not supported in flat config)

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

* fix: resolve CI issues for ESLint 10 + chai 6 upgrade

- Add .claude/** to ESLint ignores (worktree dirs were being linted)
- Remove unused eslint-disable directive in assets.ts (import-x/no-unresolved)
- Re-add @types/chai (chai 6 does not ship built-in types)
- Auto-fix prettier formatting in eslint.config.mjs

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

---------

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

Author: ryanio

.eslintrc.js

@@ -0,0 +1,92 @@
+import confusingBrowserGlobals from "confusing-browser-globals";
+import importPlugin from "eslint-plugin-import-x";
+import prettierPlugin from "eslint-plugin-prettier/recommended";
+import globals from "globals";
+import tseslint from "typescript-eslint";
+
+export default tseslint.config(
+  {
+    ignores: [
+      "docs/**",
+      "lib/**",
+      "coverage/**",
+      "src/typechain/**",
+      ".claude/**",
+    ],
+  },
+  {
+    linterOptions: {
+      reportUnusedDisableDirectives: "error",
+    },
+  },
+  tseslint.configs.recommended,
+  importPlugin.flatConfigs.errors,
+  importPlugin.flatConfigs.warnings,
+  importPlugin.flatConfigs.typescript,
+  prettierPlugin,
+  {
+    languageOptions: {
+      globals: {
+        ...globals.browser,
+        ...globals.node,
+      },
+    },
+    settings: {
+      "import-x/resolver": {
+        node: {
+          extensions: [".js", ".ts", ".tsx", ".json"],
+        },
+        typescript: {
+          alwaysTryTypes: true,
+          project: "src",
+        },
+      },
+    },
+    rules: {
+      "no-restricted-globals": ["error", ...confusingBrowserGlobals],
+      "no-restricted-imports": [
+        "error",
+        {
+          patterns: [
+            {
+              group: ["src/**", "!src/*"],
+              message: "Please use relative import for `src` files.",
+            },
+          ],
+        },
+      ],
+      curly: ["error"],
+      "@typescript-eslint/no-unused-vars": [
+        "error",
+        { argsIgnorePattern: "^_", varsIgnorePattern: "^_" },
+      ],
+      "@typescript-eslint/explicit-module-boundary-types": "off",
+      "@typescript-eslint/no-empty-interface": "off",
+      "@typescript-eslint/no-require-imports": "off",
+      "import-x/no-rename-default": "off",
+      "import-x/no-named-as-default-member": "off",
+      "import-x/order": [
+        "error",
+        {
+          groups: ["builtin", "external", "internal"],
+          "newlines-between": "never",
+          alphabetize: {
+            order: "asc",
+            caseInsensitive: true,
+          },
+        },
+      ],
+      "import-x/no-unused-modules": "off",
+      "no-control-regex": "off",
+      "object-shorthand": ["error", "always"],
+    },
+  },
+  // Test files: allow chai expressions and sinon namespace usage
+  {
+    files: ["test/**/*.ts"],
+    rules: {
+      "@typescript-eslint/no-unused-expressions": "off",
+      "import-x/namespace": "off",
+    },
+  },
+);