Implement diskpart MBR partition editor app (AI)

Create a user-space diskpart utility that can view and modify MBR
partition tables on block devices accessible through /dev.

Features:
- list: displays all 4 partition slots with type, LBA start, size
- create <slot> <type> <start> <sectors>: creates a new partition
- delete <slot>: removes a partition entry
- activate/deactivate <slot>: sets or clears the bootable flag

The tool reads sector 0 (MBR) via VFS open/read, modifies the
partition table in memory, then writes it back via open/write.
Supports hex type codes and provides human-readable type names
for common partition types (FAT12/16/32, Linux, NTFS, etc.).

Usage: diskpart hdd1 create 1 0C 2048 14336
       diskpart hdd1 list
       diskpart hdd1 delete 2

build.log

@@ -1,6 +1,9 @@
 [  3%] Building user-mode applications
 Building app: cat
   Built: /workspaces/claude-os/build/apps_bin/cat (310 bytes)
+Building app: diskpart
+/usr/bin/ld: warning: /workspaces/claude-os/build/apps_bin/diskpart.elf has a LOAD segment with RWX permissions
+  Built: /workspaces/claude-os/build/apps_bin/diskpart (8406 bytes)
 Building app: env-test
 /usr/bin/ld: warning: /workspaces/claude-os/build/apps_bin/env-test.elf has a LOAD segment with RWX permissions
   Built: /workspaces/claude-os/build/apps_bin/env-test (389 bytes)
@@ -19,9 +22,9 @@ Building app: sh
 1 warning generated.
   Built: /workspaces/claude-os/build/apps_bin/sh (3428 bytes)
 [  3%] Built target apps
+[  6%] Generating CPIO initial ramdisk
+Generated initrd: 15040 bytes
 [  6%] Built target initrd
-[  9%] Building C object src/CMakeFiles/kernel.dir/floppy.c.o
-[ 12%] Linking C executable ../bin/kernel
 [ 96%] Built target kernel
 [100%] Generating bootable ISO image
 xorriso 1.5.6 : RockRidge filesystem manipulator, libburnia project.
@@ -29,15 +32,15 @@ xorriso 1.5.6 : RockRidge filesystem manipulator, libburnia project.
 Drive current: -outdev 'stdio:/workspaces/claude-os/release/claude-os.iso'
 Media current: stdio file, overwriteable
 Media status : is blank
-Media summary: 0 sessions, 0 data blocks, 0 data,  127g free
-Added to ISO image: directory '/'='/tmp/grub.oPDKGd'
+Media summary: 0 sessions, 0 data blocks, 0 data,  126g free
+Added to ISO image: directory '/'='/tmp/grub.MJcmop'
 xorriso : UPDATE :     581 files added in 1 seconds
 Added to ISO image: directory '/'='/workspaces/claude-os/build/isodir'
 xorriso : UPDATE :     586 files added in 1 seconds
 xorriso : NOTE : Copying to System Area: 512 bytes from file '/usr/lib/grub/i386-pc/boot_hybrid.img'
-xorriso : UPDATE : Thank you for being patient. Working since 0 seconds.
-ISO image produced: 5918 sectors
-Written to medium : 5918 sectors at LBA 0
+xorriso : UPDATE :  96.99% done
+ISO image produced: 5922 sectors
+Written to medium : 5922 sectors at LBA 0
 Writing to 'stdio:/workspaces/claude-os/release/claude-os.iso' completed successfully.
 
 [100%] Built target iso