🔧 Migrate ESLint config to flat config for v10

At the moment, `npm run lint` fails outright under the ESLint v10 bump:
v9 dropped the `--ignore-path` flag and v10 removed support for the
`.eslintrc.*` format entirely, so ESLint can't even load its config.

This change ports the config to the flat `eslint.config.js` format. The
Google ruleset is a bare `rules` bag, so we can spread `google.rules`
directly rather than pulling in `FlatCompat`. The ShareDB overrides and
the ES6-option disables are carried over verbatim, `ecmaVersion` stays
at 3, and the `coverage/` ignore (previously sourced from `.gitignore`
via `--ignore-path`) moves into the config. The `lint` script drops the
removed flag and becomes a plain `eslint .`.

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

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

Author: alecgibson

.eslintrc.js eslint.config.js.eslintrc.js renamed to eslint.config.js

@@ -1,3 +1,5 @@
+var google = require('eslint-config-google');
+
 // The ESLint ecmaVersion argument is inconsistently used. Some rules will ignore it entirely, so if the rule has
 // been set, it will still error even if it's not applicable to that version number. Since Google sets these
 // rules, we have to turn them off ourselves.
@@ -37,14 +39,21 @@ var SHAREDB_RULES = {
   'valid-jsdoc': 'off'
 };
 
-module.exports = {
-  extends: 'google',
-  parserOptions: {
-    ecmaVersion: 3
+module.exports = [
+  {
+    ignores: ['node_modules/**', 'coverage/**']
   },
-  rules: Object.assign(
-    {},
-    DISABLED_ES6_OPTIONS,
-    SHAREDB_RULES
-  )
-};
+  {
+    files: ['**/*.js'],
+    languageOptions: {
+      ecmaVersion: 3,
+      sourceType: 'commonjs'
+    },
+    rules: Object.assign(
+      {},
+      google.rules,
+      DISABLED_ES6_OPTIONS,
+      SHAREDB_RULES
+    )
+  }
+];

package.json

@@ -16,7 +16,7 @@
     "nyc": "^18.0.0"
   },
   "scripts": {
-    "lint": "./node_modules/.bin/eslint --ignore-path .gitignore '**/*.js'",
+    "lint": "eslint .",
     "test": "mocha",
     "test-cover": "nyc --temp-dir=coverage -r text -r lcov npm test"
   },