Add uname, /uname and scp (key or masked password) in the Shell

- uname in the console and /uname in IRC: the firmware, its version and the chip
- scp: one file between the card and a trusted server, over SSH, with the
  device's key or a password asked (masked) in the Shell
- shared libssh helpers in src/platform/libssh_util
- README, user guide, command reference and a how-to updated

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_0162FokPdvY2KsS4NBfwyWPk

site/content/guide/irc.md

@@ -31,10 +31,13 @@ You type at the bottom; <kbd>Enter</kbd> sends. A line starting with `/` is a co
 | `/nick newnick` | Changes your nick |
 | `/topic [text]` | Shows or sets the channel topic |
 | `/names [#channel]` | Lists who is there |
+| `/uname` | Shows the firmware, its version and the chip, in this buffer only: nothing is sent |
 | `/quit [message]` | Disconnects and **stays disconnected** until you type something again |
 | `/raw …` (or `/quote`) | Sends a line to the server as it is |
 | `/settings` | The settings page |
 
+Anyone who asks the device for its CTCP `VERSION` (`/ctcp roro VERSION` in most clients) is told `roro9stack` and the firmware version.
+
 Each server, channel and private chat is a **buffer**. <kbd>Tab</kbd> moves to the next one, each shows how many messages are unread, and your own lines are in the accent colour. Scroll back with <kbd>Alt</kbd> + <kbd>;</kbd> (older) and <kbd>Alt</kbd> + <kbd>.</kbd> (newer). The up and down arrows (<kbd>Fn</kbd> + <kbd>;</kbd> and <kbd>.</kbd>) recall lines you sent.
 
 ## Mentions and the unread count