Add initial documentation and structure for DorkNet project

- Create README.md for project overview and setup instructions
- Add admin-ui/README.md for admin UI details and development setup
- Introduce client-mod/README.md explaining the MelonLoader mod functionality
- Establish docker/README.md for Docker setup and configuration
- Create docs/README.md to index project documentation
- Implement advanced-setup.md for Docker stack configuration
- Document architecture in architecture.md
- Provide easy-setup.md for hosting instructions
- Add FAQ.md for common questions and legal considerations
- Create joining-a-server.md for player connection instructions
- Establish troubleshooting.md for common issues and resolutions
- Introduce easy-app/README.md for the unified desktop application
- Add server/README.md for ASP.NET Core backend details
- Document tools/README.md for CLI helper scripts

docs/joining-a-server.md

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+# Joining someone's DorkNet server
+
+> Built for players whose friend already runs a server and gave them a
+> code. If you want to *host* instead, see [easy-setup.md](easy-setup.md).
+
+## What you'll need
+
+- A Windows PC
+- A copy of **Rec Room 2020.03.10** (your own — see
+  [Getting the 2020 client](easy-setup.md#getting-the-2020-client))
+- The join code your friend gave you (looks like `dorknet://join?...`)
+- About 2 minutes
+
+## Step 1 — Download DorkNet
+
+Grab `dorknet.exe` from the [latest release](https://github.com/YOUR_GH_USERNAME/dorknet/releases/latest).
+
+## Step 2 — First launch
+
+On the welcome screen, click **🎮 Join a server**.
+
+![first-run welcome screen — Join selected](images/first-run-welcome-join.png)
+
+## Step 3 — Paste the join code
+
+Your friend's code goes in the big text box. DorkNet decodes it and shows
+you what you're about to connect to so you can sanity-check:
+
+![join code preview](images/join-preview.png)
+
+Make sure the server name matches what your friend told you. Codes from
+strangers can point anywhere — only paste codes from people you trust.
+
+## Step 4 — Patch your Rec Room install
+
+1. Click **Browse for Rec Room install...** — point at the folder with
+   `Recroom_Release.exe`.
+2. Click **Patch & launch**.
+
+DorkNet patches the game (one-time), then launches it pointed at your
+friend's server. You'll see the normal Rec Room login screen, log in with
+the account you made on your friend's server, and you're in.
+
+---
+
+## I already patched for a different server. Can I switch?
+
+Yes — DorkNet's patcher is reversible. Click **Repair / unpatch** in the
+Patch tab to undo, then re-patch with a new join code. Or just re-run
+**Patch & launch** with the new code; the patcher detects an existing
+patch and updates the destination.
+
+## My account doesn't exist on the new server
+
+Each DorkNet server runs its own account database. You'll need to create
+a new account the first time you join a server. Your friend can sign you
+up via their admin panel, or you can use the in-game "Create account"
+flow if the server has signups enabled.
+
+## Voice chat doesn't work
+
+Voice routes through Photon Voice, which requires a separate Photon Voice
+AppId. If your friend hasn't set one up, voice chat is text-only for now.
+
+## More troubleshooting
+
+See [troubleshooting.md](troubleshooting.md).