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/shell.md

@@ -21,6 +21,7 @@ Type a command and press <kbd>Enter</kbd>. `help` lists them all; the [command r
 | `wifi status` | The network, the address, and where the DNS and time servers came from |
 | `ls /notes` | A folder of the SD card, with sizes and dates |
 | `crash` | The last crash, if there was one |
+| `uname` | The firmware, its version and the chip it is built for: `roro9stack v0.22.0 xtensa-lx7 esp32s3` |
 | `update check` | Whether a newer release exists |
 | `lora status` | What the radio is set to and what it has heard |
 
@@ -45,7 +46,7 @@ The capital is the difference: every command is in small letters, every App star
 
 ## The network
 
-For the day the network doesn't do what it should. Each of the first six takes a moment and prints as it goes; one runs at a time, and `cancel` stops it.
+For the day the network doesn't do what it should. Each of the first six takes a moment and prints as it goes, and so does `scp`; one runs at a time, and `cancel` stops it.
 
 | Command | Tells you |
 |---|---|
@@ -56,6 +57,7 @@ For the day the network doesn't do what it should. Each of the first six takes a
 | `tls git.twis.la` | A secure connection's certificate: who it is for, who signed it, until when, and **whether this device trusts it**. A port may follow (443 if not) |
 | `ntp` | A time server's clock against this device's, and how far the server is. Another server may follow |
 | `ssh user@host` | Opens the [SSH App](/guide/ssh/) and connects; `ssh status` and `ssh stop` for the session |
+| `scp /notes/a.txt user@host:docs/` | One file between the card and a server, over [SSH](/guide/ssh/#copying-a-file-scp): with the device's key, or a password asked in the Shell, masked. `cancel` stops it |
 | `ifconfig` | The interfaces (Wi-Fi, and the [VPN](/guide/vpn/) when it is up), their addresses, **which one is the default route**, and the DNS servers |
 | `arp` | The neighbours heard on the Wi-Fi: is the gateway there at all |
 | `netstat` | What the device **listens** on (updates, the Debug Console, sharing) and what is connected to it now |