feat: front button remapper (#664)

## Summary

* Custom remapper to create any variant of front button layout.

## Additional Context

* Included migration from previous frontlayout setting
* This will solve:
    *  https://github.com/crosspoint-reader/crosspoint-reader/issues/654
    * https://github.com/crosspoint-reader/crosspoint-reader/issues/652
    * https://github.com/crosspoint-reader/crosspoint-reader/issues/620
    * https://github.com/crosspoint-reader/crosspoint-reader/issues/468

<img width="860" height="1147" alt="image"
src="https://github.com/user-attachments/assets/457356ed-7a7d-4e1c-8683-e187a1df47c0"
/>



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### AI Usage

While CrossPoint doesn't have restrictions on AI tools in contributing,
please be transparent about their usage as it
helps set the right context for reviewers.

Did you use AI tools to help write this code? _**< PARTIALLY >**_

src/MappedInputManager.h

@@ -22,6 +22,8 @@ class MappedInputManager {
   bool wasAnyReleased() const;
   unsigned long getHeldTime() const;
   Labels mapLabels(const char* back, const char* confirm, const char* previous, const char* next) const;
+  // Returns the raw front button index that was pressed this frame (or -1 if none).
+  int getPressedFrontButton() const;
 
  private:
   HalGPIO& gpio;