Use vm/ instead of the hidden .vm/ as the default state directory

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

run-debian13.py

@@ -53,7 +53,7 @@ else:
     base_image = Path(result.stdout.rstrip("\n"))
     uses_shared_base_image = True
 
-state_dir = Path(env("VM_STATE_DIR") or script_dir / ".vm" / "debian13")
+state_dir = Path(env("VM_STATE_DIR") or script_dir / "vm" / "debian13")
 disk_size = env("VM_DISK_SIZE") or "20G"
 
 
@@ -124,7 +124,7 @@ def usage(stream=sys.stdout):
 Usage: {Path(sys.argv[0]).name} [--daemon] [--download-only] [--state-dir DIR] [-- QEMU_ARGUMENT ...]
 
 Start the Debian 13 virtual machine. A writable overlay is created in the state
-directory (default: .vm/debian13/), so the downloaded base image is never
+directory (default: vm/debian13/), so the downloaded base image is never
 modified. The VM hardware (memory, CPUs, SSH port forward, ...) is defined in
 qemu/debian13.ini, which is rendered to qemu.ini in the state directory and
 loaded with QEMU's -readconfig, followed by qemu/debian13-<os>-<arch>.ini (os is linux or darwin, arch is amd64 or arm64). Later
@@ -134,13 +134,13 @@ Options:
   --daemon         Run in the background while keeping the graphical window
   --download-only  Download the base image if it is missing, then exit
   --state-dir DIR  Directory for the VM disk, seed ISO and runtime files
-                   (default: .vm/debian13; overrides VM_STATE_DIR)
+                   (default: vm/debian13; overrides VM_STATE_DIR)
   -h, --help       Show this help
 
 Environment variables:
   VM_BASE_IMAGE  Base qcow2 image path (default: resolved by shared image helper)
   VM_SEED_IMAGE  cloud-init seed ISO path (default: alongside the VM disk)
-  VM_STATE_DIR   Runtime state directory (default: .vm/debian13)
+  VM_STATE_DIR   Runtime state directory (default: vm/debian13)
   VM_DISK_IMAGE  Writable overlay path
   VM_DISK_SIZE   New overlay virtual capacity (default: 20G)
   VM_IMAGE_ARCH  Guest/host architecture: arm64 or amd64 (default: auto-detected from the host)