docs: add SimpleX name registration guide (#7194)

* docs: add SimpleX name registration guide

* docs: clarify SimpleX name registration steps

Explain why registration needs two on-chain transactions with a wait
(commit-reveal prevents someone from grabbing the name mid-registration).
Mark attaching both contact and channel links as advanced usage.

* docs: switch name guide to official dapp, apply review

Use testing-names.simplex.chat and its simpler flow (both SimpleX
contact/channel fields on Create your profile; no Add profile fields
modal). Apply @epoberezkin review suggestions (intro, testing page URL,
'main names launch', claim purpose).

* Apply suggestions from code review

Co-authored-by: Evgeny <evgeny@poberezkin.com>

* docs: light screenshots, update name flow diagram

Use light-theme official-dapp screenshots. Rework the flow diagram:
drop the 'both' branch, split contact vs channel before step 4 (each
set in its own window), and match the reviewed connect wording (search
or type the name).

---------

Co-authored-by: Evgeny <evgeny@poberezkin.com>

docs/guide/README.md

@@ -12,6 +12,7 @@ The first messaging platform that has no user identifiers of any kind — 100% p
 - [Secret groups](./secret-groups.md)
 - [Channel webpage](./channel-webpage.md)
 - [Chat profiles](./chat-profiles.md)
+- [Registering a SimpleX name](./register-simplex-name.md)
 - [Managing data](./managing-data.md)
 - [Audio & video calls](./audio-video-calls.md)
 - [Privacy & security](./privacy-security.md)

docs/guide/diagrams/simplex-name-steps.mmd

@@ -0,0 +1,19 @@
+flowchart TD
+  S([Start]) --> A["Step 1: Create a wallet<br/>save your recovery phrase"]
+  A --> B["Step 2: Register the name<br/>connect wallet, search, choose years"]
+  B --> C["On Create your profile, paste your link into<br/>SimpleX contact (@name) or SimpleX channel (#name)"]
+  C --> H["Confirm: two transactions,<br/>60 seconds apart"]
+  H --> I["Step 3: search or type your name<br/>shows 'Unconfirmed name'"]
+  I --> D{"A contact or a channel?"}
+  D -->|"@name (contact)"| J1["Step 4: set Your SimpleX name<br/>in your SimpleX address"]
+  D -->|"#name (channel)"| J2["Step 4: set SimpleX name<br/>in the channel"]
+  J1 --> K["Step 5: from another device,<br/>search or type the name"]
+  J2 --> K
+  K --> Z([Connected. Name verified.])
+
+  classDef start fill:#f4ecf7,stroke:#8e44ad,color:#4a235a;
+  classDef step fill:#eaf2fb,stroke:#2e86de,color:#1b3a5b;
+  classDef ok fill:#d5f5e3,stroke:#27ae60,color:#145a32;
+  class S start;
+  class Z ok;
+  class A,B,C,H,I,J1,J2,K step;

docs/guide/register-simplex-name.md

@@ -0,0 +1,123 @@
+---
+title: Registering a SimpleX name
+---
+
+# Registering a SimpleX name
+
+A SimpleX name lets people reach you by typing a short `@name` instead of pasting
+a long link. You register the name on a website and add your SimpleX link to it,
+then claim the name in the app, to connect it with your SimpleX address or
+channel name.
+
+> Names currently run on a testing network. The registration page is
+> [testing-names.simplex.chat](https://testing-names.simplex.chat) and names end
+> in `.testing`. The steps stay the same when the main names launch.
+
+## What you need
+
+- A crypto wallet such as MetaMask.
+- The SimpleX app.
+- A link for the name to open: your **contact address** (for one-to-one chats),
+  your **channel link** (to join a channel), or both.
+
+## How it works
+
+Setting up a name takes two parts. On the website you register the name and add
+your link, so people can find your link by name. In the app you set the same name
+on your profile - to prevent any other names from opening your profile or channel.
+
+![Steps to register a SimpleX name](./diagrams/simplex-name-steps.svg)
+
+## Step 1. Create a wallet
+
+Install MetaMask (browser extension or mobile app) and create a wallet. Write
+down your recovery phrase somewhere safe and offline, as anyone with that phrase
+controls your names.
+
+On the testing network you need a small amount of test ETH to pay network fees.
+
+## Step 2. Register the name and add your link
+
+Open the registration page and tap **Connect** to link your wallet. Type the
+name you want in **Search for a name** and open it. Choose how many years to
+register for, then tap **Next**. Names are currently 6 characters or more, and
+some names are reserved.
+
+![Register your name and choose the registration period](./images/register-name.png)
+
+On **Create your profile**, paste your SimpleX link into the matching field:
+
+![Create your profile](./images/create-your-profile.png)
+
+- **SimpleX contact** for one-to-one chats. Copy your address from the app
+  (**Create SimpleX address**) and paste it here. People reach it with `@name`.
+- **SimpleX channel** for a channel. Copy your **Channel link** and paste it here.
+  People join it with `#name`.
+- **Advanced usage:** fill both to use one name for your chat (`@name`) and your
+  channel (`#name`).
+
+Then tap **Next**.
+
+Finally, tap **Begin** and complete the three steps the site shows:
+
+> Before we start. Registering your name takes three steps:
+> 1. Complete a transaction to begin the timer.
+> 2. Wait 60 seconds for the timer to complete.
+> 3. Complete a second transaction to secure your name.
+
+These two transactions protect the name you are registering. The first records
+only a secret code for the name, not the name itself, so nobody watching the
+blockchain can see which name you want. The wait lets that first transaction
+settle, and the second transaction then reveals and claims the name. Without this
+two-step process, someone could see your registration in progress and grab the
+name before you.
+
+![The three steps to secure your name](./images/before-we-start.png)
+
+## Step 3. Check what the app sees
+
+Copy your `#name.testing` (or `@name.testing`). Paste the name into the search bar, or simply type it.
+
+The app reports that the name is registered but not yet added to your profile:
+
+> Unconfirmed name. The SimpleX name is registered, but not added to profile.
+> Please add it to your address or channel profile, if you are the owner.
+
+This is expected, and confirms the name points at your link. The next step
+finishes the setup.
+
+## Step 4. Claim the name in the app
+
+Set the name on the same profile the record points at.
+
+- For your **contact address**, open your SimpleX address, tap **Your SimpleX
+  name**, enter the name, and save.
+- For your **channel**, open the channel information, tap **SimpleX name** (below
+  **Channel link**), enter the name, and save.
+
+This proves to people who connect to you that `#name.testing` (or `@name.testing`) is your name.
+
+## Step 5. Connect by name
+
+On another device, copy `#name.testing` (or `@name.testing`). Paste the name into the search bar, or simply type it. This time the app connects, and the name
+shows a check mark next to it.
+
+You can paste the name in your own device too - the app will warn you that it is your own name.
+
+Anyone can now reach you by name, and their app confirms it is really you.
+
+## If something doesn't work
+
+| Message | Meaning | Fix |
+|---|---|---|
+| Unconfirmed name | The name points at a link, but the link's profile does not claim the name yet. | Do step 4: set the name on the profile it points at. |
+| Name not found | No name is registered. | Check the spelling, or register it (step 2). |
+| No valid link | The name has no contact or channel link. | Add a link to the name on the website, on its **Records** tab. |
+| Error saving name | You tried to claim a name that has no matching link on the website. | Add your contact address or channel link to the name, then set the name again. |
+| None of your servers are set to resolve SimpleX names | No server in the app is set to resolve names. | In server settings, turn on **To resolve names** for a server. |
+
+## See also
+
+- [Making connections](./making-connections.md)
+- [Chat profiles](./chat-profiles.md)
+- [Channel webpage](./channel-webpage.md)