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

test/test_key_mapper/test_key_mapper.cpp

@@ -231,6 +231,22 @@ void test_fn_h_is_help_in_both_modes() {
     }
 }
 
+// Issue #83: Fn+p everywhere.
+void test_fn_p_is_a_screenshot_in_both_modes() {
+    for (bool typing : {true, false}) {
+        KeyMapper m;
+        m.setTextEntry(typing);
+        auto ev = press(m, withFn({'p'}));
+        TEST_ASSERT_EQUAL(1, ev.size());
+        TEST_ASSERT_EQUAL(static_cast<int>(Key::Screenshot), static_cast<int>(ev[0].key));
+        release(m);
+        ev = press(m, chars({'p'}));
+        TEST_ASSERT_EQUAL(1, ev.size());
+        TEST_ASSERT_EQUAL(static_cast<int>(Key::Char), static_cast<int>(ev[0].key));
+        TEST_ASSERT_EQUAL('p', ev[0].ch);
+    }
+}
+
 void test_plain_h_still_types() {
     for (bool typing : {true, false}) {
         KeyMapper m;
@@ -278,6 +294,7 @@ int main() {
     RUN_TEST(test_other_characters_still_type_when_not_typing);
     RUN_TEST(test_shifted_arrow_keys_type_their_symbols_when_not_typing);
     RUN_TEST(test_fn_h_is_help_in_both_modes);
+    RUN_TEST(test_fn_p_is_a_screenshot_in_both_modes);
     RUN_TEST(test_plain_h_still_types);
     RUN_TEST(test_question_mark_is_help_only_when_not_typing);
     return UNITY_END();