Show battery percentage on home screen (#167)

## Summary

* Show battery percentage on home screen
  * Moved battery rendering logic into shared ScreenComponents class
* As discussed
https://github.com/daveallie/crosspoint-reader/discussions/155

src/ScreenComponents.cpp

@@ -0,0 +1,41 @@
+#include "ScreenComponents.h"
+
+#include <GfxRenderer.h>
+
+#include <string>
+
+#include "Battery.h"
+#include "fontIds.h"
+
+void ScreenComponents::drawBattery(const GfxRenderer& renderer, const int left, const int top) {
+  // Left aligned battery icon and percentage
+  const uint16_t percentage = battery.readPercentage();
+  const auto percentageText = std::to_string(percentage) + "%";
+  renderer.drawText(SMALL_FONT_ID, left + 20, top, percentageText.c_str());
+
+  // 1 column on left, 2 columns on right, 5 columns of battery body
+  constexpr int batteryWidth = 15;
+  constexpr int batteryHeight = 10;
+  const int x = left;
+  const int y = top + 7;
+
+  // Top line
+  renderer.drawLine(x, y, x + batteryWidth - 4, y);
+  // Bottom line
+  renderer.drawLine(x, y + batteryHeight - 1, x + batteryWidth - 4, y + batteryHeight - 1);
+  // Left line
+  renderer.drawLine(x, y, x, y + batteryHeight - 1);
+  // Battery end
+  renderer.drawLine(x + batteryWidth - 4, y, x + batteryWidth - 4, y + batteryHeight - 1);
+  renderer.drawLine(x + batteryWidth - 3, y + 2, x + batteryWidth - 1, y + 2);
+  renderer.drawLine(x + batteryWidth - 3, y + batteryHeight - 3, x + batteryWidth - 1, y + batteryHeight - 3);
+  renderer.drawLine(x + batteryWidth - 1, y + 2, x + batteryWidth - 1, y + batteryHeight - 3);
+
+  // The +1 is to round up, so that we always fill at least one pixel
+  int filledWidth = percentage * (batteryWidth - 5) / 100 + 1;
+  if (filledWidth > batteryWidth - 5) {
+    filledWidth = batteryWidth - 5;  // Ensure we don't overflow
+  }
+
+  renderer.fillRect(x + 1, y + 1, filledWidth, batteryHeight - 2);
+}