scripts: automate the data-disk workflow (mkdisk / sendkeys / test-disk)

- scripts/mkdisk.sh: create the FAT32 disk with mkfs.fat -C (the flag
  that actually creates the file — plain mkfs.fat fails on a missing
  path), accept M/G/K sizes, seed seed/ files via mtools; --fresh
  re-formats, --no-seed skips seeding
- scripts/sendkeys.py: type lines into the guest via the QEMU monitor
  (US layout).  Punctuation must use QEMU's named keys (minus, slash,
  dot, ...) — bare '-', '.', '/' are not valid sendkey names, and '-'
  is the modifier separator, so they were silently dropped before
- scripts/test-disk.sh: full automated round trip — build, deploy,
  ensure image, boot headless QEMU, drive the shell (ls /disk, mkdir,
  echo >, cat, poweroff), then verify with fsck.fat (must be clean)
  and mtype (file content must have survived poweroff)
- Makefile: make disk / disk-fresh / inspect / test-disk; run, run-gui
  and debug now auto-create a missing DISK_IMG; fix the stale comment
  (mkfs.fat without -C)
- scripts/boot.sh: auto-create a missing DISK_IMG via mkdisk.sh
- seed/: motd.txt + lines.txt seeded onto fresh images
- Verified end to end: ./scripts/test-disk.sh --fresh passes

2 files changed, 17 insertions, 0 deletions

diff --git a/seed/lines.txt b/seed/lines.txt
new file mode 100644
index 0000000..719197f
--- /dev/null
+++ b/seed/lines.txt
@@ -0,0 +1,6 @@
+the quick brown fox jumps over the lazy dog
+the quick brown fox jumps over the lazy dog
+the quick brown fox jumps over the lazy dog
+line 4: a slightly longer line to exercise multi-cluster reads
+line 5: rs-dos persistence test — power off and back on
+line 6: hello from the disk
diff --git a/seed/motd.txt b/seed/motd.txt
new file mode 100644
index 0000000..ac960fa
--- /dev/null
+++ b/seed/motd.txt
@@ -0,0 +1,11 @@
+Welcome to rs-dos!
+
+This file lives on the FAT32 data disk (the one mounted at /disk).
+The kernel mounts the first valid FAT32 volume it finds — create or
+re-seed this image with:
+
+    make disk            # create if missing (default /tmp/disk.img)
+    make disk-fresh      # re-format + re-seed from seed/
+
+Everything written from the shell survives reboots: it's a real disk,
+not RAM.