Keep generated template previews out of photo selection

tests/test_photo_sources.py

@@ -0,0 +1,19 @@
+def test_uploaded_photos_exclude_generated_templates_before_limit(client, service):
+    photo = service.assets.put(b"fixture", "family.jpg", "images")
+    for _ in range(5):
+        service.assets.put(b"fixture", "quote.jpg", "generated")
+    response = client.get("/api/v1/assets?source=uploaded&limit=1")
+    assert response.status_code == 200
+    assert response.json()[0]["asset_id"] == photo["asset_id"]
+    assert response.json()[0]["source"] == "uploaded"
+    generated = client.get("/api/v1/assets?source=generated").json()
+    assert len(generated) == 5 and all(a["source"] == "generated" for a in generated)
+    assert len(client.get("/api/v1/assets").json()) == 6
+
+
+def test_filename_does_not_determine_photo_source(client, service):
+    service.assets.put(b"fixture", "weather.jpg", "images")
+    assert (
+        client.get("/api/v1/assets?source=uploaded").json()[0]["name"] == "weather.jpg"
+    )
+    assert client.get("/api/v1/assets?source=invalid").status_code == 422