fix: handle custom logo images without alpha channel

cv2.imread with IMREAD_UNCHANGED loads the image as-is, but the code
unconditionally indexes channel 3 (birdseye_logo[:, :, 3]) assuming
RGBA format. This crashes with IndexError for:

- Grayscale PNGs (2D array, no channel dimension)
- RGB PNGs without alpha (3 channels, no index 3)
- Fully transparent PNGs saved as grayscale+alpha (2 channels)

Handle all image formats:
- 2D (grayscale): use directly as luminance
- 4+ channels (RGBA): extract alpha channel (existing behavior)
- 3 channels (RGB/BGR): convert to grayscale

Also fixes the shape[0]/shape[1] swap in the array slice that breaks
non-square images (related to #6802, #7863).

frigate/output/birdseye.py

@@ -303,12 +303,20 @@ class BirdsEyeFrameManager:
                 birdseye_logo = cv2.imread(logo_files[0], cv2.IMREAD_UNCHANGED)
 
         if birdseye_logo is not None:
-            transparent_layer = birdseye_logo[:, :, 3]
+            if birdseye_logo.ndim == 2:
+                # Grayscale image (no channels) — use directly as luminance
+                transparent_layer = birdseye_logo
+            elif birdseye_logo.shape[2] >= 4:
+                # RGBA — use alpha channel as luminance
+                transparent_layer = birdseye_logo[:, :, 3]
+            else:
+                # RGB or other format without alpha — convert to grayscale
+                transparent_layer = cv2.cvtColor(birdseye_logo, cv2.COLOR_BGR2GRAY)
             y_offset = height // 2 - transparent_layer.shape[0] // 2
             x_offset = width // 2 - transparent_layer.shape[1] // 2
             self.blank_frame[
-                y_offset : y_offset + transparent_layer.shape[1],
-                x_offset : x_offset + transparent_layer.shape[0],
+                y_offset : y_offset + transparent_layer.shape[0],
+                x_offset : x_offset + transparent_layer.shape[1],
             ] = transparent_layer
         else:
             logger.warning("Unable to read Frigate logo")