Replace SpoolBuddy self-update with SSH-based updates from Bambuddy

The daemon's self-update mechanism (git fetch/reset on its own code) was
  fragile: .git permission errors, self-modifying code mid-run, hardcoded
  main branch. Bambuddy now SSHes into the SpoolBuddy Pi and drives the
  update remotely — matching its own branch, with step-by-step progress
  via WebSocket. Install script updated with SSH access, sudoers entry,
  and --ssh-pubkey flag for pairing.

Dockerfile

@@ -25,6 +25,7 @@ RUN apt-get update && apt-get install -y --no-install-recommends \
     ffmpeg \
     iproute2 \
     libcap2-bin \
+    openssh-client \
     && rm -rf /var/lib/apt/lists/*
 
 # Allow binding to privileged ports (e.g. 990/FTPS) as non-root user.