api: serve pdfs from SFTP for trainer UI

backend/api.py

@@ -9,6 +9,7 @@ from dotenv import load_dotenv
 from fastapi import FastAPI, HTTPException, Response
 from fastapi.middleware.cors import CORSMiddleware
 from fastapi.responses import FileResponse
+from backend.sftp_store import download_bytes
 from backend.sftp_store import SFTPStore
 
 
@@ -103,7 +104,21 @@ def root() -> Dict[str, str]:
 
 @app.get("/api/pdf/{pdf_id}")
 def get_pdf(pdf_id: str):
-    store = SFTPStore()
+    # Read PDF bytes from SFTP: /inserio/pdfs/{pdf_id}.pdf
+    rel = f"pdfs/{pdf_id}.pdf"
+    try:
+        data = download_bytes(rel)
+    except FileNotFoundError:
+        raise HTTPException(status_code=404, detail="pdf not found")
+    except Exception as e:
+        raise HTTPException(status_code=500, detail=f"sftp read failed: {e}")
+
+    # Stream bytes back to UI
+    resp = PlainTextResponse(content=data)
+    resp.media_type = "application/pdf"
+    resp.headers["X-PDF-Name"] = f"{pdf_id}.pdf"
+    return resp
+
     remote_rel = f"pdfs/{pdf_id}.pdf"
     if not store.exists(remote_rel):
         raise HTTPException(status_code=404, detail="PDF not found")