Notes: edit a text file of any size (#47)

The editor held the whole note in memory and stopped at 16 KB. It now keeps
a window of the file around the cursor, and the rest on the card as a list
of pieces (notes::NoteDocument). Memory with a note open is what it was.

Up to 64 KB a save rewrites the file, as before. Above, the five-second
save appends what changed to <note>.edit, and the file is rewritten on
leaving the note, with a progress bar. After a power cut, opening the note
picks the edit up where it was saved; a rewrite cut short is finished or
dropped, never half applied.

Also: Ctrl with Fn+Up/Down go to the start and end of the note; the
consoles' `key` command takes ctrl-, alt- and shift-; the Storage App's
`e` no longer refuses a big file.

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

src/services/power_service.cpp

@@ -42,6 +42,7 @@ void PowerService::applyScreen(ScreenState state) {
 }
 
 void PowerService::powerOff() {
+    poweringOff_ = true;
     if (beforePowerOff) beforePowerOff();
     auto& display = M5Cardputer.Display;
     display.wakeup();

src/services/power_service.h

@@ -28,6 +28,7 @@ class PowerService : public Service {
 
     // Run before the device powers off: the last chance to put on the card what's only in memory.
     std::function<void()> beforePowerOff;
+    bool poweringOff() const { return poweringOff_; }  // from beforePowerOff on: no time for long work
 
    private:
     void applyScreen(ScreenState state);
@@ -38,6 +39,7 @@ class PowerService : public Service {
     PowerButton button_{2000};
     ScreenState applied_ = ScreenState::On;
     int appliedBrightness_ = -1;
+    bool poweringOff_ = false;
 };
 
 }  // namespace roro