Add official account info page and client screenshots

Introduces a new documentation page explaining the Matrix.org (Official Account) user, how to identify it, and what to do if you receive suspicious messages. Includes example screenshots for different clients to help users verify the official account.

The purpose is to support using Server Notices more extensively on the matrix.org homeserver. This new page will be referred in the topic of the server notices room.

n.b currently the server notices room is titled Server Alerts and has a different avatar, but these will be changed at the same time as putting this page live.

content/official.md

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+title = "Matrix.org (Official Account)"
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+
+## Who is the Matrix.org (Official Account) <code>@server:matrix.org</code>?
+
+The Matrix.org Foundation uses <code>@server:matrix.org</code> to message users on the matrix.org homeserver. It is a special account, used to send information from the server to registered users.
+
+<div style="text-align: center; padding: .4em 1em; background-color: #ffcb006b;">
+We will <b>never</b> ask for your personal information or password
+</div>
+
+## Why am I in a room called Matrix.org (Official Account)?
+
+We invite users to this room when you first register your account. For long-term users, we started inviting you in June 2025. We use this room to send you information about your account on the matrix.org homeserver.
+
+Note: You can't send a message to this room.
+
+## How can I tell that this is the official account in my Matrix client or app?
+
+You can verify that the message is from the official account by checking the Matrix user ID of the sender. The user ID should match <code>@sender:matrix.org</code> exactly.
+
+How to check this depends on the client or app you use. Typically you need to click or tap the profile or avatar of the user.
+
+Here are some examples of how it looks in some common apps:
+
+![Profile](/images/official/client1.png)
+![Avatar](/images/official/client3.png)
+![Tooltip](/images/official/client2.png)
+
+## What should I do if the user ID doesn’t match?
+
+If you receive a message pretending to be the official account, you should report the message immediately. If you are a matrix.org user, you can use the "report user" function in your app or client to let us know.
+
+If your client doesn't provide a way to do this, or if you are on a different homeserver, then please email us at [abuse@matrix.org](mailto:abuse@matrix.org) with the details.