Switch to native Claude Code installer and add update command

Replace the deprecated npm installation with the native installer. The
binary is installed to /usr/local/bin so it survives the home directory
bind mount at runtime.

Add a 'claude update' subcommand that rebuilds the image with the latest
Claude Code binary and removes all existing containers.

Disable the in-container auto-updater since the binary lives in the
read-only image layer.

Dockerfile

@@ -13,13 +13,22 @@ RUN pacman -Syu --noconfirm \
         ripgrep \
         nodejs \
         npm \
+        curl \
         sudo && \
     groupadd -g ${GID} ${USERNAME} && \
     useradd -m -u ${UID} -g ${GID} -s /bin/bash ${USERNAME} && \
     echo "${USERNAME} ALL=(ALL) NOPASSWD: ALL" >> /etc/sudoers && \
-    npm install -g @anthropic-ai/claude-code && \
     pacman -Scc --noconfirm
 
+# Install Claude Code using the native installer, then copy the binary
+# to a system-wide location so it survives the home directory bind mount
+USER ${USERNAME}
+WORKDIR /tmp
+RUN curl -fsSL https://claude.ai/install.sh | bash && \
+    sudo cp ~/.local/bin/claude /usr/local/bin/claude && \
+    rm -rf ~/.local/share/claude ~/.local/bin/claude ~/.claude ~/.claude.json \
+           ~/.cache/claude
+
 USER ${USERNAME}
 
 WORKDIR /home/${USERNAME}