fix(gateway): load the proxy routes and ticket settings in every environment

The YARP routes, the bucket path transform and the StreamTicket section only
existed in appsettings.Development.json, so a Production run had no routes at
all and every /media request fell through to a 404. Move them to
appsettings.json and leave only the environment-specific overrides (key path)
in the Development file; the container gets the filer address, the bucket and
the allowed CORS origins from environment variables.

backend/Musify.StreamingGateway/appsettings.Development.json

@@ -1,32 +1,5 @@
 {
   "StreamTicket": {
-    "PublicKeyPath": "D:\\weed\\stream_public.pem",
-    "Audience": "media-gateway",
-    "Issuer": "musify-webapi",
-    "QueryParameterName": "t",
-    "MediaPathPrefix": "/media"
-  },
-
-  "Cors": {
-    "AllowedOrigins": [ "http://localhost:5173", "http://localhost:3000" ]
-  },
-
-  "ReverseProxy": {
-    "Routes": {
-      "media": {
-        "ClusterId": "seaweed-filer",
-        "Match": { "Path": "/media/{**rest}" },
-        "Transforms": [
-          { "PathPattern": "/buckets/webapi-storage/{**rest}" }
-        ]
-      }
-    },
-    "Clusters": {
-      "seaweed-filer": {
-        "Destinations": {
-          "filer": { "Address": "http://localhost:8888/" }
-        }
-      }
-    }
+    "PublicKeyPath": "../../deploy/keys/stream_public.pem"
   }
 }

backend/Musify.StreamingGateway/appsettings.json

@@ -6,5 +6,36 @@
       "Yarp": "Information"
     }
   },
-  "AllowedHosts": "*"
+  "AllowedHosts": "*",
+
+  "StreamTicket": {
+    "PublicKeyPath": "",
+    "Audience": "media-gateway",
+    "Issuer": "musify-webapi",
+    "QueryParameterName": "t",
+    "MediaPathPrefix": "/media"
+  },
+
+  "Cors": {
+    "AllowedOrigins": []
+  },
+
+  "ReverseProxy": {
+    "Routes": {
+      "media": {
+        "ClusterId": "seaweed-filer",
+        "Match": { "Path": "/media/{**rest}" },
+        "Transforms": [
+          { "PathPattern": "/buckets/webapi-storage/{**rest}" }
+        ]
+      }
+    },
+    "Clusters": {
+      "seaweed-filer": {
+        "Destinations": {
+          "filer": { "Address": "http://localhost:8888/" }
+        }
+      }
+    }
+  }
 }