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>

tsconfig.base.json

@@ -0,0 +1,24 @@
+{
+  "$schema": "https://json.schemastore.org/tsconfig",
+  "compilerOptions": {
+    "target": "ES2022",
+    "lib": ["ES2023"],
+    "module": "ESNext",
+    "moduleResolution": "Bundler",
+    "moduleDetection": "force",
+    "resolveJsonModule": true,
+    "esModuleInterop": true,
+    "isolatedModules": true,
+    "verbatimModuleSyntax": true,
+    "strict": true,
+    "noUncheckedIndexedAccess": true,
+    "noImplicitOverride": true,
+    "noUnusedLocals": true,
+    "noUnusedParameters": true,
+    "skipLibCheck": true,
+    "forceConsistentCasingInFileNames": true,
+    "declaration": true,
+    "declarationMap": true,
+    "sourceMap": true
+  }
+}