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

src/tools/index.ts

@@ -8,6 +8,7 @@ import './coolify';
 import './agent';
 import './memory';
 import './skills';
+import './prd';
 
 // Re-export the public API — identical surface to the old tools.ts
 export { ALL_TOOLS, executeTool, ToolDefinition } from './registry';