feat: USB CDC ACM virtual serial console

[deasmi]

This PR adds support for exposing a virtual serial port to the host, that can be used as a serial console tty. This was done as a POC as it seemed like it should be possible and it was interesting.

It is 100% written by Claude. please bear that in mind.

It includes some things that Claude used to run the development process, like the deploy.sh script.

Therefore I am not suggesting this is merged directly, I am providing it as a POC to prove it is possible as this would be a nice feature to add.

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Exposes a CDC ACM virtual serial port to the attached host via a /boot/usb.acm boot flag, providing an out-of-band text console for OPNsense/FreeBSD/Linux servers over the existing NanoKVM USB cable. Host enumerates /dev/ttyACM0 (Linux) or /dev/cuaU0 (FreeBSD).

The SG2002/dwc2 USB controller's FIFO budget only fits keyboard + mouse + ACM simultaneously. The toggle therefore implies HID-Only mode and additionally suppresses the touchpad. The UI warns of the trade-off and reboots to apply.

Components:

• kvmapp/system/init.d/S03usbhid: when /boot/usb.acm exists, skip hid.GS2 (touchpad) and link functions/acm.GS0 into configs/c.1/. Standard-mode S03usbdev is untouched.
• server/service/vm/virtual-device.go: USB Serial toggle dispatched via existing POST /api/vm/device/virtual (device:"serial"). Enable forces the hid-only script over /etc/init.d/S03usbdev, writes /boot/usb.acm, removes firmware's acm::respawn getty from /etc/inittab (so web terminal has exclusive ttyGS0 access), and reboots. Disable removes the flag, restores the getty line, and reboots.
• server/service/hid/status.go: exports CopyModeFile so vm package can force the script swap, bypassing the bcdDevice-based short-circuit in SwitchMode.
• server/proto/vm.go: GetVirtualDeviceRsp gains Serial bool.
• web Settings -> Device: third Switch + warning modal.
• web Terminal -> Serial Port: /dev/ttyGS0 radio option when enabled.
• web Terminal -> terminal/index.tsx: picocom with --imap lfcrlf (fixes diagonal output) and --noreset (avoids ENOTTY on exit).
• Makefile + docker/Dockerfile: fix make app on Apple Silicon / arm64 Linux.
• deploy.sh: dev workflow helper (build + deploy over SSH).
• i18n: real English strings; placeholder stubs in 23 other locales.

Tested on NanoKVM Lite (SG2002) against OPNsense/FreeBSD.