fix: use node:16-bullseye-slim to fix apt repos and canvas compat

node:16-slim defaults to Debian Buster (EOL), breaking apt-get.
node:20-slim breaks canvas@2.8.0 (no pre-built binary for Node 20).
node:16-bullseye-slim: active Bullseye apt repos + Node 16 ABI
that canvas@2.8.0 was built for.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: colevandersWands

Dockerfile

@@ -1,8 +1,8 @@
 # syntax = docker/dockerfile:1
 
 # Adjust NODE_VERSION as desired
-ARG NODE_VERSION=20
-FROM node:${NODE_VERSION}-slim AS base
+ARG NODE_VERSION=16
+FROM node:${NODE_VERSION}-bullseye-slim AS base
 
 LABEL fly_launch_runtime="Node.js"