Support swapping the functionality of the front buttons (#133)

## Summary

**What is the goal of this PR?** 

Adds a setting to swap the front buttons. The default functionality are:
Back/Confirm/Left/Right. When this setting is enabled they become:
Left/Right/Back/Confirm. This makes it more comfortable to use when
holding in your right hand since your thumb can more easily rest on the
next button. The original firmware has a similar setting.

**What changes are included?**

- Add the new setting.
- Create a mapper to dynamically switch the buttons based on the
setting.
- Use mapper on the various activity screens.
- Update the button hints to reflect the swapped buttons.

## Additional Context

Full disclosure: I used Codex CLI to put this PR together, but did
review it to make sure it makes sense.

Also tested on my device:
https://share.cleanshot.com/k76891NY

src/activities/boot_sleep/BootActivity.h

@@ -3,6 +3,7 @@
 
 class BootActivity final : public Activity {
  public:
-  explicit BootActivity(GfxRenderer& renderer, InputManager& inputManager) : Activity("Boot", renderer, inputManager) {}
+  explicit BootActivity(GfxRenderer& renderer, MappedInputManager& mappedInput)
+      : Activity("Boot", renderer, mappedInput) {}
   void onEnter() override;
 };

src/activities/boot_sleep/SleepActivity.h

@@ -5,8 +5,8 @@ class Bitmap;
 
 class SleepActivity final : public Activity {
  public:
-  explicit SleepActivity(GfxRenderer& renderer, InputManager& inputManager)
-      : Activity("Sleep", renderer, inputManager) {}
+  explicit SleepActivity(GfxRenderer& renderer, MappedInputManager& mappedInput)
+      : Activity("Sleep", renderer, mappedInput) {}
   void onEnter() override;
 
  private: