Android: a customisable key bar, a quick-access keyboard, a long-press cursor gesture, and a side panel on tablets

The key bar above the software keyboard is now the user's own: which keys, in what order, up to sixteen
in two rows that never scroll. Ctrl and Alt latch across the bar and the phone's keyboard, and Ctrl or Alt
with a cursor key sends the modified CSI form. Seven predefined groups (essentials, cursor, control,
symbols, tmux, vim, function) and keys of one's own, written in \e / ^C notation, are arranged on a
customise sheet that saves as it goes.

A grid button swaps the software keyboard for a quick-access keyboard of the same height, with KEYS,
SNIPPETS, HISTORY and APPEARANCE tabs; it reopens to the tab last used. Snippets go through the shell's
existing InsertSnippet. History keeps a typed command only once the remote has echoed it, so nothing
typed at a password prompt is ever recorded; it is memory-only and LOCK clears it. Each session pump now
keeps its last kilobyte of output and the alternate-screen state for that test (OutputTail).

Long-press and drag on the terminal sends arrow keys, as a joystick with three speeds by distance;
scrolling is unchanged and there is no mode switch. It takes the touch before Chromium's own long press,
so a held finger no longer pastes; paste is on the bar by default instead. A switch in APPEARANCE turns
the gesture off. The text-size buttons moved from the bar to APPEARANCE.

On wide screens the same tabs open as a side panel beside the terminal, toggled from the top bar, with
the bar's own keys repeated at the top of KEYS while the bar stands down.

The model, gesture arithmetic, echo reading and history are in DodoSSH.Client.Shell and covered by
TerminalKeyboardTests and OutputTailTests. Builds clean; not yet exercised on a device, because the
emulator's install is locked behind a passphrase that was not recorded.

src/DodoSSH.Client.Terminal/TerminalSessionPump.cs

@@ -167,6 +167,10 @@ public sealed class TerminalSessionPump : IAsyncDisposable
     /// <summary>Bytes read from the remote and not yet sent to the renderer.</summary>
     public int BytesPending => backlog.Buffered;
 
+    /// <summary>The last of what the remote wrote, for the phone's command history.</summary>
+    /// <remarks>See <see cref="OutputTail"/> for why a client keeps any of it.</remarks>
+    public OutputTail Recent { get; } = new();
+
     /// <summary>Total frames sent to the renderer, for the throughput harness.</summary>
     public long FramesSent { get; private set; }
 
@@ -353,6 +357,7 @@ public sealed class TerminalSessionPump : IAsyncDisposable
                 }
 
                 BytesRead += read;
+                Recent.Append(buffer.AsSpan(0, read));
 
                 // Copied out of the rented buffer, because the backlog holds it until the renderer has
                 // room and the next read is already about to overwrite this one.