fix(build): make the packed image actually bootable

There were three independent reasons a fresh build produced an image that
OVMF would not boot. All three are fixed here; verified by booting the
resulting ISO/deshab-dev.img under QEMU/OVMF through to FirstInit.

1. ESP rejected by OVMF (CODE/linux/pack_system_image.sh)
   The vfat formatter was invoked with an explicit -s 8, forcing 4KiB clusters.
   On the 256MiB ESP that yields exactly 65535 clusters - the FAT32 0xFFF5
   boundary - and OVMF's FatPkg refuses to mount the volume. Symptom: BdsDxe
   logs "failed to load ... Not Found", the ESP shows up as BLKn with no FS in
   the UEFI Shell, and the firmware falls through to the internal shell.
   The sidecar FAT32 image (make_sata_sidecar.sh) mounts fine because it calls
   the formatter without -s. Drop -s here too and let the tool pick geometry.
   Do NOT add -f 1: OVMF mounts nfat=1 and nfat=2 alike, it was not the cause.

2. Limine dropped into a panic (CODE/linux/pack_system_image.sh)
   limine.conf declares the Linux-compat guest modules. build.sh uncomments
   them once Linux has been built, but nothing ever comments them back, so the
   file says "load boot():/boot/linux-initrd.img" while only linux-bzImage
   exists on disk - Limine panics on the missing module and never reaches the
   kernel. Filter the guest module_path lines against SYSTEM/boot/ at pack
   time and write the result to the ESP. Both the root /limine.conf and
   /limine/limine.conf are written, since Limine 10 prefers the latter. The
   tracked source file is left untouched.

3. Nine drivers were never compiled (build.ps1)
   Commit 055c521 untracked the .drv binaries on the grounds that they are
   regenerable, but build.ps1 only ever invoked Build-DkmDriver for 8 of the
   17 drivers listed in manifest.json. timer/acpi/pci/ahci/bootfs/vfs/fat32/
   devfs/ps2kbd had sources under CODE/DKM/ and no build step, so the image
   shipped without them and Limine failed on the first one. Add the missing
   compile steps, grouped by load stage. All 17 now match manifest.json.

Also in this commit (environment/tooling hygiene):
- check_env.sh: stop hardcoding /mnt/d/Code/Deshab (the original author's
  machine); derive the repo root from the script's own location. It was
  reporting a bogus "wsl_mount" failure on every other checkout and sending
  people to install packages that were already present. Also check and
  advertise the image-packing tools (dosfstools/e2fsprogs/fdisk/rsync), which
  were missing from the dependency list even though pack_system_image.sh
  hard-requires them.
- build_initrd.sh: same hardcoded-path fix.
- README.md: relative path instead of the stale absolute one.

Verified: ./build.bat -Variant dev under WSL2/Ubuntu, then QEMU/OVMF boots
through BdsDxe -> Limine -> UTSM -> DKM (17/17) -> DSK -> FirstInit, with the
PS/2 mouse initialising cleanly.

build.ps1

@@ -961,20 +961,40 @@ foreach ($tool in $toolApps) {
 Write-Host '[build] Building DKM framebuffer driver...'
 Build-DkmDriver (Join-Path $Root 'CODE\DKM\console_fb\console_fb.c') (Join-Path $SystemDir 'driver\console\console_fb.drv')
 
+# stage0: platform + bus — timer 提供 PIT 校准，acpi 枚举 RSDP/XSDT，pci 扫描配置空间。
+# 这三个驱动 manifest.json 里是必需的；055c521 把它们从 git 移除后此处必须重新编译，
+# 否则 limine 会 panic「Failed to open module boot():/driver/platform/timer.drv」。
+Write-Host '[build] Building DKM platform/bus drivers...'
+Build-DkmDriver (Join-Path $Root 'CODE\DKM\timer\timer.c') (Join-Path $SystemDir 'driver\platform\timer.drv')
+Build-DkmDriver (Join-Path $Root 'CODE\DKM\acpi\acpi.c')   (Join-Path $SystemDir 'driver\platform\acpi.drv')
+Build-DkmDriver (Join-Path $Root 'CODE\DKM\pci\pci.c')     (Join-Path $SystemDir 'driver\bus\pci.drv')
+
 # B7: apic.drv 纳入构建 (原 platform/apic.drv 为预置二进制, 不随 apic.c 更新)
 Write-Host '[build] Building DKM platform apic driver...'
 Build-DkmDriver (Join-Path $Root 'CODE\DKM\apic\apic.c') (Join-Path $SystemDir 'driver\platform\apic.drv')
 
 Write-Host '[build] Building DKM storage drivers...'
+Build-DkmDriver (Join-Path $Root 'CODE\DKM\ahci\ahci.c') (Join-Path $SystemDir 'driver\block\ahci.drv')
 Build-DkmDriver (Join-Path $Root 'CODE\DKM\nvme\nvme.c') (Join-Path $SystemDir 'driver\block\nvme.drv')
 Build-DkmDriver (Join-Path $Root 'CODE\DKM\ehci\ehci.c') (Join-Path $SystemDir 'driver\block\ehci.drv')
 Build-DkmDriver (Join-Path $Root 'CODE\DKM\xhci\xhci.c') (Join-Path $SystemDir 'driver\block\xhci.drv')
 
+# stage2: filesystem — bootfs 挂 boot module，vfs 汇总，fat32 只读 FAT32，devfs 暴露 /dev。
+Write-Host '[build] Building DKM filesystem drivers...'
+Build-DkmDriver (Join-Path $Root 'CODE\DKM\bootfs\bootfs.c') (Join-Path $SystemDir 'driver\fs\bootfs.drv')
+Build-DkmDriver (Join-Path $Root 'CODE\DKM\vfs\vfs.c')       (Join-Path $SystemDir 'driver\fs\vfs.drv')
+Build-DkmDriver (Join-Path $Root 'CODE\DKM\fat32\fat32.c')   (Join-Path $SystemDir 'driver\fs\fat32.drv')
+Build-DkmDriver (Join-Path $Root 'CODE\DKM\devfs\devfs.c')   (Join-Path $SystemDir 'driver\fs\devfs.drv')
+
 Write-Host '[build] Building DKM network drivers...'
 Build-DkmDriver (Join-Path $Root 'CODE\DKM\e1000\e1000.c') (Join-Path $SystemDir 'driver\net\e1000.drv')
 Build-DkmDriver (Join-Path $Root 'CODE\DKM\virtio_net\virtio_net.c') (Join-Path $SystemDir 'driver\net\virtio_net.drv')
 Build-DkmDriver (Join-Path $Root 'CODE\DKM\ath9k\ath9k.c') (Join-Path $SystemDir 'driver\net\ath9k.drv')
 
+# stage3: input — ps2kbd 注册 IRQ1。
+Write-Host '[build] Building DKM input drivers...'
+Build-DkmDriver (Join-Path $Root 'CODE\DKM\ps2kbd\ps2kbd.c') (Join-Path $SystemDir 'driver\input\ps2kbd.drv')
+
 Write-Host "[build] Output: $Output"
 Write-Host "[build] DSK Output: $DskOutput"
 Write-Host "[build] Variant: $Variant"