Screenshots: Fn+p on every screen (#83)

Fn+p saves the screen as it is to /screenshots, as the Shell's `screenshot`
does, from anywhere: text fields, dialogs and the help panel included. The
key never reaches an App.

It refuses on Settings > Debug Console, which shows the token: a picture of
that page is a copy of the token in a file (App::showsSecret). `key shot`
presses it over the consoles.

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

lib/input/src/key_mapper.cpp

@@ -106,6 +106,13 @@ void KeyMapper::onChar(char c, const RawKeys& keys, std::vector<KeyEvent>& out)
                     return;
                 }
                 break;
+            case 'p':
+            case 'P':
+                if (keys.fn) {  // Fn+p: a screenshot, while typing too
+                    out.push_back(KeyEvent::of(Key::Screenshot));
+                    return;
+                }
+                break;
             case '?':
                 if (!textEntry_ && !keys.fn) {  // ? alone, when it wouldn't be typed
                     out.push_back(KeyEvent::of(Key::Help));