feat(storage): ext4-only disk via mkfs.ext4 -d; drop FAT16; feature-gated mount (ro on unknown ro_compat); ext4 read spans blocks, delete clears inode, mkdir counts dir; virtio-blk writes; test-qemu e2fsck gate

crates/types/src/spawn.rs

@@ -9,7 +9,7 @@
 use crate::budget::Limits;
 
 pub const SPAWN: usize = 0;
-/// Program file names: FAT 8.3, with room to spare.
+/// The longest program file name a spawn request carries.
 pub const MAX_NAME: usize = 16;
 /// Where init puts the child's stack top (its stack ends at the image).
 pub const STACK_TOP: usize = 0x10000;