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/util/KeyboardEntryActivity.h

@@ -1,6 +1,5 @@
 #pragma once
 #include <GfxRenderer.h>
-#include <InputManager.h>
 #include <freertos/FreeRTOS.h>
 #include <freertos/semphr.h>
 #include <freertos/task.h>
@@ -31,7 +30,7 @@ class KeyboardEntryActivity : public Activity {
   /**
    * Constructor
    * @param renderer Reference to the GfxRenderer for drawing
-   * @param inputManager Reference to InputManager for handling input
+   * @param mappedInput Reference to MappedInputManager for handling input
    * @param title Title to display above the keyboard
    * @param initialText Initial text to show in the input field
    * @param startY Y position to start rendering the keyboard
@@ -40,11 +39,11 @@ class KeyboardEntryActivity : public Activity {
    * @param onComplete Callback invoked when input is complete
    * @param onCancel Callback invoked when input is cancelled
    */
-  explicit KeyboardEntryActivity(GfxRenderer& renderer, InputManager& inputManager, std::string title = "Enter Text",
-                                 std::string initialText = "", const int startY = 10, const size_t maxLength = 0,
-                                 const bool isPassword = false, OnCompleteCallback onComplete = nullptr,
-                                 OnCancelCallback onCancel = nullptr)
-      : Activity("KeyboardEntry", renderer, inputManager),
+  explicit KeyboardEntryActivity(GfxRenderer& renderer, MappedInputManager& mappedInput,
+                                 std::string title = "Enter Text", std::string initialText = "", const int startY = 10,
+                                 const size_t maxLength = 0, const bool isPassword = false,
+                                 OnCompleteCallback onComplete = nullptr, OnCancelCallback onCancel = nullptr)
+      : Activity("KeyboardEntry", renderer, mappedInput),
         title(std::move(title)),
         text(std::move(initialText)),
         startY(startY),