The bare `mcables` pattern in .gitignore (line 11) and .dockerignore
(line 18) was intended to ignore the built binary at the repo root, but
without a leading slash it also matched the cmd/mcables/ directory. The
result: cmd/mcables/main.go was never tracked in git, and fresh worktrees
had to copy it from a sibling to build.
- Change `mcables` → `/mcables` in both files (still ignores the root
binary; no longer matches the cmd subdirectory).
- Add cmd/mcables/main.go (copied from picasso's worktree, verified
identical to head's main checkout).
Verified: `git check-ignore cmd/mcables/main.go` returns not-ignored;
a touched `./mcables` at the repo root is still ignored via `/mcables`.
`go build ./...` clean.
