fix(grub): fix bitmap error and menu rendering

- Convert bee-logo.png to RGBA (color type 6) and strip all metadata
  chunks (cHRM, bKGD, tIME, tEXt) that confuse GRUB's minimal PNG parser
- Move terminal_output gfxterm before insmod png / theme load so the
  theme initialises in an active gfxterm context
- Remove echo ASCII art banner from grub.cfg — with gfxterm active and
  no terminal_box in the theme, echo output renders over the menu area
- Fix icon_heigh typo → icon_height; increase item_height 16→20 with
  item_padding 0→2 for reliable text rendering in boot_menu

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

iso/builder/config/bootloaders/grub-efi/live-theme/theme.txt

@@ -34,11 +34,11 @@ terminal-font: "Unifont Regular 16"
         item_font = "Unifont Regular 16"
         selected_item_color= "#f5a800"
         selected_item_font = "Unifont Regular 16"
-        item_height = 16
-        item_padding = 0
+        item_height = 20
+        item_padding = 2
         item_spacing = 4
         icon_width = 0
-        icon_heigh = 0
+        icon_height = 0
         item_icon_space = 0
 }