fix: anchor the .dockerignore binary pattern

The previous commit renamed .Dockerignore to .dockerignore but missed
staging this content fix: an unanchored "domogeek" pattern excludes any
path named domogeek anywhere in the build context, including the
cmd/domogeek source directory itself, not just the compiled binary at
the repo root.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Hu8wwahgecuCGfesTKCfEd

.dockerignore

@@ -1,2 +1,2 @@
-domogeek
+/domogeek
 .git