SSH client: a terminal on another machine (#2)

The SSH App opens one session to a shell, over libssh (LibSSH-ESP32 5.10.0)
on mbedTLS. A server is trusted the first time on its fingerprint, and a
changed key is a warning with Cancel selected. The password is typed each
time and kept nowhere; or the device makes itself an Ed25519 key, whose
public half is shown, written to /ssh/id_ed25519.pub and printed by
`ssh status`.

lib/term is the terminal: what a shell, less, top, nano and vim send, with
sixteen colours, scroll regions, the alternate screen and 100 lines of
scrollback. Five text sizes with Ctrl and + or -, from 60x20 to 26x8, told
to the far end. The session goes on when the App is left; SSH shows in the
Status Bar. `ssh user@host` in the Shell opens the App.

Also:
- Keys that aren't characters carry Shift, Ctrl and Alt. The terminal needs
  it, and it makes Ctrl+Fn+up/down in a note and Shift+Tab in Gemini work
  from the real keyboard.
- IRC doesn't try to connect under 60 KB free: started with a session open,
  its TLS handshake took the heap down to 236 bytes.
- libssh's own curve25519 is left out of the build (scripts/libssh_filter.py):
  libsodium's has the same names.

Costs 292 KB of flash and about 50 KB of heap while a session is open; not
started under 75 KB free.

Docs: guide page, how-to, FAQ, home page, Status Bar, SD card folders, the
memory how-to, README, glossary, N1 notes with Q254 to Q266 and the checks.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01EhqxQ49eCju4CzKYNjZzwT

lib/core/src/app_keys.h

@@ -313,6 +313,34 @@ inline constexpr KeyHelp kVpn[] = {
     {"; .", "up, down"},
 };
 
+// ssh: SSH, the hosts
+inline constexpr KeyHelp kSsh[] = {
+    {"Enter", "connect, open"},
+    {"; .", "up, down"},
+    {"n", "a new connection"},
+    {"d", "forget this host"},
+};
+
+// ssh-terminal: SSH, the terminal
+inline constexpr KeyHelp kSshTerminal[] = {
+    {"`", "Esc"},
+    {"Alt `", "a backtick"},
+    {"Fn ; . , /", "the arrows"},
+    {"Fn Shift ; .", "Page Up, Page Down"},
+    {"Ctrl a..z", "Ctrl+C and the rest"},
+    {"Alt ; .", "scroll back, forward"},
+    {"Ctrl + -", "larger, smaller text"},
+    {"Ctrl Alt q", "disconnect"},
+    {"Fn `", "leave it running"},
+};
+
+// ssh-key: SSH, this device's key
+inline constexpr KeyHelp kSshKey[] = {
+    {"Enter", "make a key, or a new one"},
+    {"w", "write the public half to the card"},
+    {"`", "back"},
+};
+
 // notes: Notes, the list
 inline constexpr KeyHelp kNotes[] = {
     {"; .", "up, down"},