feat: add ESLint with error-handling rules

Add ESLint v9.35+ with typescript-eslint recommended config and
error-handling rules: preserve-caught-error (enforces { cause } when
re-throwing), no-unused-vars with caughtErrors:all, and
eslint-plugin-no-catch-all (warns on catch blocks that don't rethrow).

Fix existing violations: add error cause to container-runtime rethrow,
prefix unused vars with underscore, remove unused imports.

https://claude.ai/code/session_01JPjzhBp9PR5LtfLWVDrYrH

eslint.config.js

@@ -0,0 +1,32 @@
+import globals from 'globals'
+import pluginJs from '@eslint/js'
+import tseslint from 'typescript-eslint'
+import noCatchAll from 'eslint-plugin-no-catch-all'
+
+export default [
+  { ignores: ['node_modules/', 'dist/', 'container/', 'groups/'] },
+  { files: ['src/**/*.{js,ts}'] },
+  { languageOptions: { globals: globals.node } },
+  pluginJs.configs.recommended,
+  ...tseslint.configs.recommended,
+  {
+    plugins: { 'no-catch-all': noCatchAll },
+    rules: {
+      'preserve-caught-error': ['error', { requireCatchParameter: true }],
+      '@typescript-eslint/no-unused-vars': [
+        'error',
+        {
+          args: 'all',
+          argsIgnorePattern: '^_',
+          caughtErrors: 'all',
+          caughtErrorsIgnorePattern: '^_',
+          destructuredArrayIgnorePattern: '^_',
+          varsIgnorePattern: '^_',
+          ignoreRestSiblings: true,
+        },
+      ],
+      'no-catch-all/no-catch-all': 'warn',
+      '@typescript-eslint/no-explicit-any': 'warn',
+    },
+  },
+]