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

src/ui/fonts.h

@@ -8,6 +8,9 @@ namespace fontdata {
 extern const uint8_t _6x13_tf[];
 extern const uint8_t _6x13B_tf[];
 extern const uint8_t _5x8_tf[];
+extern const uint8_t _4x6_tf[];
+extern const uint8_t _6x10_tf[];
+extern const uint8_t _9x15_tf[];
 }  // namespace fontdata
 
 // Latin-1 bitmap fonts (accented letters included).
@@ -15,6 +18,9 @@ namespace fonts {
 inline const lgfx::U8g2font body(fontdata::_6x13_tf);   // 6x13
 inline const lgfx::U8g2font bold(fontdata::_6x13B_tf);  // 6x13 bold
 inline const lgfx::U8g2font small(fontdata::_5x8_tf);   // 5x8, Status Bar
+inline const lgfx::U8g2font tiny(fontdata::_4x6_tf);    // 4x6: the terminal's smallest (issue #2)
+inline const lgfx::U8g2font medium(fontdata::_6x10_tf); // 6x10
+inline const lgfx::U8g2font large(fontdata::_9x15_tf);  // 9x15
 }  // namespace fonts
 
 }  // namespace roro