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/atlas.d.ts

@@ -0,0 +1,21 @@
+import { LLMMessage } from './llm';
+import { ToolContext } from './tools';
+export declare function clearAtlasSession(sessionId: string): void;
+export declare function listAtlasSessions(): {
+    id: string;
+    messages: number;
+    prdReady: boolean;
+    createdAt: string;
+    lastActiveAt: string;
+}[];
+export interface AtlasChatResult {
+    reply: string;
+    sessionId: string;
+    history: LLMMessage[];
+    /** Set when Atlas has called finalize_prd — contains the full PRD markdown */
+    prdContent: string | null;
+    model: string;
+}
+export declare function atlasChat(sessionId: string, userMessage: string, ctx: ToolContext, opts?: {
+    preloadedHistory?: LLMMessage[];
+}): Promise<AtlasChatResult>;