feat: overhaul container initialization and entrypoint

- Replace apt-get with apt in Dockerfile
- Add tini as init system and set ENTRYPOINT/CMD
- Simplify init.fish by removing first-run logic and tmux session management
- Add landing.fish and SIGTERM signal handling
- Improve container lifecycle management

Dockerfile

@@ -5,14 +5,17 @@ RUN git clone https://github.com/iceBear67/bubble .
 FROM debian:13
 COPY --from=0 --chmod=0755 /src/bubble.sh /bin/bubble
 RUN <<EOF
-apt-get update && apt-get upgrade
+apt update
+apt upgrade
 chmod +x /bin/bubble
-apt-get install -y curl jq neovim htop fish tmux sudo git iproute2 iputils-ping dnsutils openssh-sftp-server build-essential htop
+apt install curl jq neovim htop fish tmux sudo git iproute2 iputils-ping dnsutils openssh-sftp-server build-essential htop tini
 useradd -m -s /usr/bin/fish user
 echo "user ALL=(ALL:ALL) NOPASSWD:ALL" >> /etc/sudoers
 sudo -u user mkdir -p /home/user/.config/fish/
 ln -s /usr/lib/openssh/sftp-server /usr/sbin/bubble-sftp
 EOF
 COPY ./init.fish /init.fish
+COPY ./landing.fish /landing.fish
 COPY --chown=user ./user.fish /home/user/.config/fish/config.fish
-
+ENTRYPOINT ["/usr/bin/tini", "--"]
+CMD ["/usr/bin/fish", "/init.fish"]