chore: set up pnpm workspace tooling

Root package.json with workspace scripts, pnpm-workspace.yaml, shared
tsconfig base, ESLint flat config, Prettier, editorconfig, .nvmrc, and
.env.example covering LiveKit/Gemini/GitHub/Atlas/Voyage.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

eslint.config.mjs

@@ -0,0 +1,18 @@
+import js from '@eslint/js';
+import tseslint from 'typescript-eslint';
+
+export default tseslint.config(
+  {
+    ignores: ['**/dist/**', '**/build/**', '**/node_modules/**', '**/*.config.*'],
+  },
+  js.configs.recommended,
+  ...tseslint.configs.recommended,
+  {
+    rules: {
+      '@typescript-eslint/no-unused-vars': [
+        'warn',
+        { argsIgnorePattern: '^_', varsIgnorePattern: '^_' },
+      ],
+    },
+  },
+);