fix(grub): replace em-dash with ASCII -- in all menu entry titles

Em-dash (U+2014) renders as garbage on GRUB serial/SOL output
(IPMI BMC consoles). Replace with ASCII double-hyphen throughout
grub.cfg template, write_canonical_grub_cfg, and theme.txt comment.

Also align template grub.cfg structure with write_canonical_grub_cfg:
toram entry moved to top level (was inside submenu).

bible: add ascii-safe-text contract documenting the no-em-dash rule.

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

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

@@ -5,7 +5,7 @@ title-text: ""
 message-font: "Unifont Regular 16"
 terminal-font: "Unifont Regular 16"
 
-#bee logo — centered, upper third of screen
+#bee logo - centered, upper third of screen
 + image {
         top = 4%
         left = 50%-200