added read-only mode + visual improvements

pages/api/v1/collections/[id].ts

@@ -19,9 +19,21 @@ export default async function collections(
       .status(collections.status)
       .json({ response: collections.response });
   } else if (req.method === "PUT") {
+    if (process.env.DEMO_MODE === "true")
+      return res.status(400).json({
+        response:
+          "This action is disabled because this is a read-only demo of Linkwarden.",
+      });
+
     const updated = await updateCollectionById(user.id, collectionId, req.body);
     return res.status(updated.status).json({ response: updated.response });
   } else if (req.method === "DELETE") {
+    if (process.env.DEMO_MODE === "true")
+      return res.status(400).json({
+        response:
+          "This action is disabled because this is a read-only demo of Linkwarden.",
+      });
+
     const deleted = await deleteCollectionById(user.id, collectionId);
     return res.status(deleted.status).json({ response: deleted.response });
   }

pages/api/v1/collections/index.ts

@@ -16,6 +16,12 @@ export default async function collections(
       .status(collections.status)
       .json({ response: collections.response });
   } else if (req.method === "POST") {
+    if (process.env.DEMO_MODE === "true")
+      return res.status(400).json({
+        response:
+          "This action is disabled because this is a read-only demo of Linkwarden.",
+      });
+
     const newCollection = await postCollection(req.body, user.id);
     return res
       .status(newCollection.status)