feat: add Atlas PRD agent for product discovery

- src/prompts/atlas.ts — full Atlas system prompt (6-phase PM discovery flow)
- src/tools/prd.ts — finalize_prd tool that signals PRD completion
- src/agents/atlas.ts — Atlas agent config (Tier A, conversational)
- src/atlas.ts — atlasChat() multi-turn session handler
- server.ts — /atlas/chat, /atlas/sessions endpoints

Made-with: Cursor

dist/agents/atlas.js

@@ -0,0 +1,10 @@
+"use strict";
+Object.defineProperty(exports, "__esModule", { value: true });
+const registry_1 = require("./registry");
+(0, registry_1.registerAgent)({
+    name: 'Atlas',
+    description: 'PRD agent — guides users through structured product discovery and produces a comprehensive requirements document',
+    model: 'A', // Gemini Flash — fast, conversational, cost-effective for dialogue
+    promptId: 'atlas',
+    tools: (0, registry_1.pick)(['finalize_prd'])
+});