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>

.prettierignore

@@ -0,0 +1,6 @@
+node_modules
+dist
+build
+pnpm-lock.yaml
+.omc
+*.log