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/network/CrossPointWebServerActivity.cpp

@@ -57,7 +57,7 @@ void CrossPointWebServerActivity::onEnter() {
   // Launch network mode selection subactivity
   Serial.printf("[%lu] [WEBACT] Launching NetworkModeSelectionActivity...\n", millis());
   enterNewActivity(new NetworkModeSelectionActivity(
-      renderer, inputManager, [this](const NetworkMode mode) { onNetworkModeSelected(mode); },
+      renderer, mappedInput, [this](const NetworkMode mode) { onNetworkModeSelected(mode); },
       [this]() { onGoBack(); }  // Cancel goes back to home
       ));
 }
@@ -141,7 +141,7 @@ void CrossPointWebServerActivity::onNetworkModeSelected(const NetworkMode mode)
 
     state = WebServerActivityState::WIFI_SELECTION;
     Serial.printf("[%lu] [WEBACT] Launching WifiSelectionActivity...\n", millis());
-    enterNewActivity(new WifiSelectionActivity(renderer, inputManager,
+    enterNewActivity(new WifiSelectionActivity(renderer, mappedInput,
                                                [this](const bool connected) { onWifiSelectionComplete(connected); }));
   } else {
     // AP mode - start access point
@@ -174,7 +174,7 @@ void CrossPointWebServerActivity::onWifiSelectionComplete(const bool connected)
     exitActivity();
     state = WebServerActivityState::MODE_SELECTION;
     enterNewActivity(new NetworkModeSelectionActivity(
-        renderer, inputManager, [this](const NetworkMode mode) { onNetworkModeSelected(mode); },
+        renderer, mappedInput, [this](const NetworkMode mode) { onNetworkModeSelected(mode); },
         [this]() { onGoBack(); }));
   }
 }
@@ -305,7 +305,7 @@ void CrossPointWebServerActivity::loop() {
     }
 
     // Handle exit on Back button
-    if (inputManager.wasPressed(InputManager::BTN_BACK)) {
+    if (mappedInput.wasPressed(MappedInputManager::Button::Back)) {
       onGoBack();
       return;
     }
@@ -428,5 +428,6 @@ void CrossPointWebServerActivity::renderServerRunning() const {
                               REGULAR);
   }
 
-  renderer.drawButtonHints(UI_FONT_ID, "« Exit", "", "", "");
+  const auto labels = mappedInput.mapLabels("« Exit", "", "", "");
+  renderer.drawButtonHints(UI_FONT_ID, labels.btn1, labels.btn2, labels.btn3, labels.btn4);
 }