refactor(build): rename docker-images/glm52-int4-int8 to glm52
Shorter, matches the sparkrun-vllm-ds4-gb10:glm52 tag it produces and the recipes/glm52 family. The dir holds the int4-int8 overlay for the glm52 image, not a single recipe; the old name implied a 1:1 recipe mapping that never held. No behavior change — same Dockerfile, same build.sh, same output tag; only the docker_image_dir references (2 active, 1 commented) and the Dockerfile build-path comment move with it.