fix: tons of little things and workarounds

[tulilirockz]

This fixes tons of little thingies scattered about. Some stylistic, but this should change:

• uv/pixi to GDX instead of also being on dx too
• simplified the sed expression we had to get the compose repos
• tries to make tailscale work by having /var/tmp on the image build
• sets the default hostname to bluefin instead of... nothing?

[hanthor]

cp: cannot overwrite directory '/./usr/bin' with non-directory '/var/tmp/system_files_overrides/gdx/./usr/bin'
Error: building at STEP "RUN --mount=type=tmpfs,dst=/tmp --mount=type=bind,from=config,src=/rpms,dst=/tmp/rpms /var/tmp/build_scripts/build.sh": while running runtime: exit status 1

GDX failed

[tulilirockz]

Yeah, seems to need some more work