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/apps/ssh_app.h

@@ -0,0 +1,71 @@
+#pragma once
+
+#include <memory>
+#include <string>
+#include <vector>
+
+#include "app.h"
+#include "dialog_model.h"
+#include "line_editor.h"
+#include "list_model.h"
+#include "services/ssh_service.h"
+#include "services/storage_service.h"
+#include "settings.h"
+#include "ui/canvas.h"
+
+namespace roro {
+
+// The SSH App (issue #2, docs/milestones/N1.md): the saved hosts, and a terminal on the one that
+// is connected. Leaving it with Home doesn't end the session; coming back finds it.
+class SshApp : public App {
+   public:
+    static constexpr const char* kPublicKeyPath = "/ssh/id_ed25519.pub";
+
+    SshApp(SshService& ssh, Settings& settings, StorageService& storage) : ssh_(ssh), settings_(settings), storage_(storage) {}
+
+    void onEnter() override;
+    bool onKey(const KeyEvent& e) override;
+    bool textEntryActive() const override { return view_ == View::Entry || (view_ == View::Session && !dialog_); }
+    void help(std::vector<KeyHelp>& out) const override;
+    const char* helpTitle() const override;
+    void update(uint32_t nowMs) override;
+    void draw(Canvas& c) override;
+
+    // `ssh user@host` from the Shell or a console: "" or why not.
+    std::string connectTo(const std::string& target);
+
+   private:
+    enum class View { Hosts, Entry, Session, Key };
+    struct Font {
+        const lgfx::IFont* font;
+        int w, h;
+    };
+    static const Font kFonts[5];
+
+    void grid(int& cols, int& rows) const;
+    void connect(const term::SshTarget& target);
+    void setFont(int index);
+    bool sessionKey(const KeyEvent& e);
+    void drawHosts(Canvas& c);
+    void drawSession(Canvas& c);
+    void drawTerminal(Canvas& c);
+    void drawKey(Canvas& c);
+    void say(const std::string& text);
+    void writePublicKey();
+
+    SshService& ssh_;
+    Settings& settings_;
+    StorageService& storage_;
+    View view_ = View::Hosts;
+    ListModel list_{8};
+    std::vector<std::string> hosts_;
+    LineEditor entry_{96}, password_{96};
+    std::unique_ptr<DialogModel> dialog_;
+    enum class Ask { None, Trust, NewKey, Forget } ask_ = Ask::None;
+    SshService::State shownState_ = SshService::State::Idle;
+    std::string message_;
+    uint32_t messageMs_ = 0, shownRevision_ = 0, lastDrawMs_ = 0;
+    int font_ = 1, scroll_ = 0;
+};
+
+}  // namespace roro