Print via Brother BR-Script3 PostScript instead of the vendor driver

The HL-4150CDN emulates PostScript 3, so CUPS converts client documents to PostScript and forwards them to socket://<ip>:9100. The official BR-Script3 PPD turns device options (tray, duplex, colour, media type, toner save, ...) into setpagedevice instructions. This drops the i386 multiarch runtime and the broken Brother vendor filter chain, and removes the unused Brother Linux packages from the repo.

.containerignore

@@ -0,0 +1,6 @@
+# Keep version-control metadata and macOS junk out of the build context.
+.jj
+.git
+.opencode
+.DS_Store
+**/.DS_Store