feat(fs): Complete full FAT32 storage filesystem driver, auto-mount at /mnt/fat32, and add df & mkfs.vfat tools

boot/stage2.asm

@@ -93,7 +93,7 @@ start2:
     mov word [kernel_dap_seg], 0x1000
     mov dword [kernel_dap_lba], 16
     mov dword [kernel_dap_lba + 4], 0
-    mov cx, 12                         ; 12 chunks * 64 sectors = 768 sectors (384 KB)
+    mov cx, 6                          ; 6 chunks * 64 sectors = 384 sectors (192 KB)
 
 .kernel_chunk_loop:
     push cx
@@ -196,10 +196,10 @@ pm_entry:
     mov ss, ax
     mov esp, 0x7C00
 
-    ; Copy kernel from 0x10000 to 0x100000 (1MB mark) - 384 KB (768 sectors)
+    ; Copy kernel from 0x10000 to 0x100000 (1MB mark) - 192 KB (384 sectors)
     mov esi, 0x10000
     mov edi, 0x100000
-    mov ecx, (768 * 512) / 4
+    mov ecx, (384 * 512) / 4
     rep movsd
 
     ; Enable PAE in CR4