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/core/storage.py

@@ -0,0 +1,61 @@
+from __future__ import annotations
+
+from app.core.config import settings
+
+_s3_client = None
+
+
+def get_s3_client():
+    global _s3_client
+    if _s3_client is None:
+        import boto3
+
+        _s3_client = boto3.client(
+            "s3",
+            endpoint_url=settings.s3_endpoint,
+            aws_access_key_id=settings.s3_access_key,
+            aws_secret_access_key=settings.s3_secret_key,
+            region_name=settings.s3_region,
+        )
+    return _s3_client
+
+
+def ensure_bucket() -> None:
+    if settings.storage_mode != "s3":
+        return
+    client = get_s3_client()
+    bucket = settings.s3_bucket
+    try:
+        client.head_bucket(Bucket=bucket)
+    except Exception:
+        client.create_bucket(Bucket=bucket)
+
+
+def upload_object(key: str, body: bytes, content_type: str) -> None:
+    if settings.storage_mode == "memory":
+        memory_store[key] = (body, content_type)
+        return
+    client = get_s3_client()
+    ensure_bucket()
+    client.put_object(
+        Bucket=settings.s3_bucket,
+        Key=key,
+        Body=body,
+        ContentType=content_type,
+    )
+
+
+def download_object(key: str) -> tuple[bytes, str] | None:
+    if settings.storage_mode == "memory":
+        return memory_store.get(key)
+    client = get_s3_client()
+    try:
+        response = client.get_object(Bucket=settings.s3_bucket, Key=key)
+        body = response["Body"].read()
+        content_type = response.get("ContentType", "application/octet-stream")
+        return body, content_type
+    except Exception:
+        return None
+
+
+memory_store: dict[str, tuple[bytes, str]] = {}