feat(sleep): pre-calculate EPUB cover dimensions for FIT/CROP modes

- Add JpegToBmpConverter::getJpegDimensions() to extract JPEG dimensions
- Fix getCoverBmpPath() ternary operator precedence bug
- Pre-calculate exact dimensions per mode:
  * FIT: width=480px, height=(480*jpegHeight)/jpegWidth
  * CROP: height=800px, width=(800*jpegWidth)/jpegHeight
- Generate separate cache files (cover_fit.bmp vs cover_crop.bmp)
- Eliminates runtime scaling artifacts, improves sleep screen clarity

lib/Epub/Epub.cpp

@@ -425,8 +425,7 @@ const std::string& Epub::getLanguage() const {
 }
 
 std::string Epub::getCoverBmpPath(bool cropped) const {
-  const auto coverFileName = "cover" + cropped ? "_crop" : "";
-  return cachePath + "/" + coverFileName + ".bmp";
+  return cropped ? (cachePath + "/cover_crop.bmp") : (cachePath + "/cover_fit.bmp");
 }
 
 bool Epub::generateCoverBmp(bool cropped) const {
@@ -462,12 +461,37 @@ bool Epub::generateCoverBmp(bool cropped) const {
       return false;
     }
 
+    // Get JPEG dimensions to calculate target dimensions for FIT/CROP
+    int jpegWidth, jpegHeight;
+    if (!JpegToBmpConverter::getJpegDimensions(coverJpg, jpegWidth, jpegHeight)) {
+      Serial.printf("[%lu] [EBP] Failed to get JPEG dimensions\n", millis());
+      coverJpg.close();
+      return false;
+    }
+
+    // Calculate target dimensions based on FIT/CROP mode
+    // FIT: ancho fijo 480px, alto proporcional = 480 * (jpegHeight / jpegWidth)
+    // CROP: alto fijo 800px, ancho proporcional = 800 * (jpegWidth / jpegHeight)
+    int targetWidth, targetHeight;
+    if (cropped) {
+      // CROP mode: height = 800, width proportional
+      targetHeight = 800;
+      targetWidth = (800 * jpegWidth) / jpegHeight;
+    } else {
+      // FIT mode: width = 480, height proportional
+      targetWidth = 480;
+      targetHeight = (480 * jpegHeight) / jpegWidth;
+    }
+
+    Serial.printf("[%lu] [EBP] Calculated %s dimensions: %dx%d (original JPEG: %dx%d)\n", millis(),
+                  cropped ? "CROP" : "FIT", targetWidth, targetHeight, jpegWidth, jpegHeight);
+
     FsFile coverBmp;
     if (!SdMan.openFileForWrite("EBP", getCoverBmpPath(cropped), coverBmp)) {
       coverJpg.close();
       return false;
     }
-    const bool success = JpegToBmpConverter::jpegFileToBmpStream(coverJpg, coverBmp);
+    const bool success = JpegToBmpConverter::jpegFileToBmpStreamWithSize(coverJpg, coverBmp, targetWidth, targetHeight);
     coverJpg.close();
     coverBmp.close();
     SdMan.remove(coverJpgTempPath.c_str());

lib/JpegToBmpConverter/JpegToBmpConverter.cpp

@@ -565,3 +565,32 @@ bool JpegToBmpConverter::jpegFileTo1BitBmpStreamWithSize(FsFile& jpegFile, Print
                                                          int targetMaxHeight) {
   return jpegFileToBmpStreamInternal(jpegFile, bmpOut, targetMaxWidth, targetMaxHeight, true);
 }
+
+// Get JPEG dimensions without full conversion
+bool JpegToBmpConverter::getJpegDimensions(FsFile& jpegFile, int& width, int& height) {
+  // Reset file position to beginning
+  if (!jpegFile.seek(0)) {
+    Serial.printf("[%lu] [JPG] Failed to seek to beginning of JPEG file\n", millis());
+    return false;
+  }
+
+  // Initialize JPEG decoder
+  pjpeg_image_info_t imageInfo = {};
+  JpegReadContext context{jpegFile, {}, 0, 0};
+
+  const int decodeStatus = pjpeg_decode_init(&imageInfo, jpegReadCallback, &context, false);
+  if (decodeStatus != 0) {
+    Serial.printf("[%lu] [JPG] pjpeg_decode_init failed with status %d\n", millis(), decodeStatus);
+    return false;
+  }
+
+  // Get dimensions from image info
+  width = imageInfo.m_width;
+  height = imageInfo.m_height;
+
+  Serial.printf("[%lu] [JPG] Read JPEG dimensions: %dx%d\n", millis(), width, height);
+
+  // Reset file position after reading
+  jpegFile.seek(0);
+  return true;
+}

lib/JpegToBmpConverter/JpegToBmpConverter.h

@@ -16,4 +16,6 @@ class JpegToBmpConverter {
   static bool jpegFileToBmpStreamWithSize(FsFile& jpegFile, Print& bmpOut, int targetMaxWidth, int targetMaxHeight);
   // Convert to 1-bit BMP (black and white only, no grays) for fast home screen rendering
   static bool jpegFileTo1BitBmpStreamWithSize(FsFile& jpegFile, Print& bmpOut, int targetMaxWidth, int targetMaxHeight);
+  // Get JPEG dimensions without full conversion
+  static bool getJpegDimensions(FsFile& jpegFile, int& width, int& height);
 };