Persist Atlas chat history; fix re-greeting on refresh

- GET /api/projects/[id]/atlas-chat returns stored user+assistant messages
- POST handles __atlas_init__ trigger: runs once when no history exists,
  not stored as a user turn so Atlas intro appears cleanly
- Rewrite AtlasChat.tsx: fully self-contained component with own message
  state; loads history from DB on mount, only greets on first open
- Remove assistant-ui runtime dependency for message persistence
- Add Vision & Success Metrics, Integrations & Dependencies, Open Questions
  to PRD section tracker (now 12 sections matching the PDF)

Made-with: Cursor

app/[workspace]/project/[projectId]/prd/page.tsx

@@ -6,13 +6,16 @@ import { useParams } from "next/navigation";
 const PRD_SECTIONS = [
   { id: "executive_summary",    label: "Executive Summary" },
   { id: "problem_statement",    label: "Problem Statement" },
+  { id: "vision_metrics",       label: "Vision & Success Metrics" },
   { id: "users_personas",       label: "Users & Personas" },
   { id: "user_flows",           label: "User Flows" },
   { id: "feature_requirements", label: "Feature Requirements" },
   { id: "screen_specs",         label: "Screen Specs" },
   { id: "business_model",       label: "Business Model" },
+  { id: "integrations",         label: "Integrations & Dependencies" },
   { id: "non_functional",       label: "Non-Functional Reqs" },
-  { id: "risks",                label: "Risks" },
+  { id: "risks",                label: "Risks & Mitigations" },
+  { id: "open_questions",       label: "Open Questions" },
 ];
 
 interface PRDSection {