feat(backend): scaffold PodMan agent pipeline + token server

Express server with /health and a LiveKit token endpoint. Module skeletons
for the full loop: vision (Gemini), GitHub fusion, collision detector (pure,
testable), intervention engine, and continual-learning memory store. Approve
native build scripts (esbuild/genai/protobufjs) at the workspace root.

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

backend/src/env.ts

@@ -0,0 +1,39 @@
+import 'dotenv/config';
+
+/** Reads an env var, throwing if it is required but missing. */
+function read(name: string, required = false): string {
+  const value = process.env[name] ?? '';
+  if (required && !value) {
+    throw new Error(`Missing required env var: ${name}`);
+  }
+  return value;
+}
+
+export const env = {
+  port: Number(process.env.PORT ?? 8787),
+
+  livekit: {
+    url: read('LIVEKIT_URL'),
+    apiKey: read('LIVEKIT_API_KEY'),
+    apiSecret: read('LIVEKIT_API_SECRET'),
+  },
+
+  gemini: {
+    apiKey: read('GEMINI_API_KEY'),
+    visionModel: process.env.GEMINI_VISION_MODEL ?? 'gemini-3.5-flash',
+    liveModel: process.env.GEMINI_LIVE_MODEL ?? '',
+  },
+
+  github: {
+    token: read('GITHUB_TOKEN'),
+    repo: read('GITHUB_REPO'),
+  },
+
+  mongo: {
+    uri: read('MONGODB_URI'),
+  },
+
+  voyage: {
+    apiKey: read('VOYAGE_API_KEY'),
+  },
+} as const;