Stop forcing DOCKER_HOST to tcp://docker.local:2375

Job containers already mount the host Docker socket and default to
unix:///var/run/docker.sock. The TCP override is unreachable from the
bridge network and breaks docker login/build in Gitea Actions.

Co-authored-by: Cursor <cursoragent@cursor.com>

README.md

@@ -53,4 +53,4 @@ jobs:
 - **Multi-platform** builds via QEMU (if platforms != linux/amd64)
 - **Layer caching** via local buildx cache
 - **Git metadata** — auto-adds `date-SHA` tag + git tag if on a tag ref
-- **`DOCKER_HOST`** — auto-configured for Gitea Actions (`tcp://docker.local:2375`)
+- Uses the job-mounted Docker socket (`unix:///var/run/docker.sock`) provided by the Gitea runner