feat: Initial support for the x3 (#875)

## Summary

Adds Xteink X3 hardware support to CrossPoint Reader. The X3 uses the
same SSD1677 e-ink controller as the X4 but with a different panel
(792x528 vs 800x480), different button layout, and an I2C fuel gauge
(BQ27220) instead of ADC-based battery reading.

All X3-specific behavior is gated by runtime device detection — X4
behavior is unchanged.

Depends on community-sdk X3 support: open-x4-epaper/community-sdk#19
(merged).

## Changes

### HAL Layer

**HalGPIO** (`lib/hal/HalGPIO.cpp/.h`)
- I2C-based device fingerprinting at boot: probes for BQ27220 fuel
gauge, DS3231 RTC, and QMI8658 IMU to distinguish X3 from X4
- Detection result cached in NVS for fast subsequent boots
- Exposes `deviceIsX3()` / `deviceIsX4()` helpers used throughout the
codebase
- X3 button mapping (7 GPIOs vs X4's layout)
- USB connection detection and wake classification for X3

**HalDisplay** (`lib/hal/HalDisplay.cpp/.h`)
- Calls `einkDisplay.setDisplayX3()` before init when X3 is detected
- Requests display resync after power button / flash wake events
- Runtime display dimension accessors (`getDisplayWidth()`,
`getDisplayHeight()`, `getBufferSize()`)
- Exposed as global `display` instance for use by image converters

**HalPowerManager** (`lib/hal/HalPowerManager.cpp/.h`)
- X3 battery reading via I2C fuel gauge (BQ27220 at 0x55, SOC register)
- X3 power button uses GPIO hold for deep sleep

### Display & Rendering

**GfxRenderer** (`lib/GfxRenderer/GfxRenderer.cpp/.h`)
- Buffer size and display dimensions are now runtime values (not
compile-time constants) to support both panel sizes
- X3 anti-aliasing tuning: only the darker grayscale level is applied to
avoid washed-out text on the X3 panel. X4 retains both levels via
`deviceIsX4()` gate

**Image Converters** (`lib/JpegToBmpConverter`, `lib/PngToBmpConverter`)
- Cover image prescale target uses runtime display dimensions from HAL
instead of hardcoded 800x480

### UI Themes

**BaseTheme / LyraTheme** (`src/components/themes/`)
- X3 button position mapping for the different physical layout
- Adjusted UI element positioning for 792x528 viewport

### Boot & Init

**main.cpp**
- X3 hardware detection logging
- Adjusted init sequence for X3 (no `HalSystem::begin()` dependency on
X3 path)

**HomeActivity**
- Uses runtime `renderer.getBufferSize()` instead of static
`GfxRenderer::getBufferSize()`

FYI I did not add support for the gyro page turner. That can be it's own
PR.

lib/PngToBmpConverter/PngToBmpConverter.cpp

@@ -1,5 +1,6 @@
 #include "PngToBmpConverter.h"
 
+#include <HalDisplay.h>
 #include <HalStorage.h>
 #include <InflateReader.h>
 #include <Logging.h>
@@ -16,8 +17,6 @@ constexpr bool USE_8BIT_OUTPUT = false;
 constexpr bool USE_ATKINSON = true;
 constexpr bool USE_FLOYD_STEINBERG = false;
 constexpr bool USE_PRESCALE = true;
-constexpr int TARGET_MAX_WIDTH = 480;
-constexpr int TARGET_MAX_HEIGHT = 800;
 // ============================================================================
 
 // BMP writing helpers (same as JpegToBmpConverter)
@@ -822,7 +821,10 @@ bool PngToBmpConverter::pngFileToBmpStreamInternal(FsFile& pngFile, Print& bmpOu
 }
 
 bool PngToBmpConverter::pngFileToBmpStream(FsFile& pngFile, Print& bmpOut, bool crop) {
-  return pngFileToBmpStreamInternal(pngFile, bmpOut, TARGET_MAX_WIDTH, TARGET_MAX_HEIGHT, false, crop);
+  // Use runtime display dimensions (swapped for portrait cover sizing)
+  const int targetWidth = display.getDisplayHeight();
+  const int targetHeight = display.getDisplayWidth();
+  return pngFileToBmpStreamInternal(pngFile, bmpOut, targetWidth, targetHeight, false, crop);
 }
 
 bool PngToBmpConverter::pngFileToBmpStreamWithSize(FsFile& pngFile, Print& bmpOut, int targetMaxWidth,