Update admin theme/layout and refresh README details.

Align the project baseline with the latest admin interface styling and layout structure while documenting setup and usage updates in README.

apps/api/app/modules/media/router.py

@@ -0,0 +1,24 @@
+from fastapi import APIRouter, HTTPException, Query
+from fastapi.responses import Response
+
+from app.core.media_signing import verify_signed_media
+from app.core.storage import download_object
+
+router = APIRouter()
+
+
+@router.get("/files/{file_path:path}")
+async def get_media_file(
+    file_path: str,
+    expires: int = Query(...),
+    sig: str = Query(...),
+):
+    if not file_path.startswith("avatars/"):
+        raise HTTPException(status_code=404, detail="FILE_NOT_FOUND")
+    if not verify_signed_media(file_path, expires, sig):
+        raise HTTPException(status_code=403, detail="INVALID_SIGNATURE")
+    stored = download_object(file_path)
+    if not stored:
+        raise HTTPException(status_code=404, detail="FILE_NOT_FOUND")
+    body, content_type = stored
+    return Response(content=body, media_type=content_type)