fix(orbit): forward --help to the Orbit binary once it is installed

Description

glab orbit --help, -h, and bare glab orbit showed glab's static text, with remote/local examples that Orbit 0.121.0 removed. They now forward to the Orbit binary. If the binary is not installed, glab keeps its own text, so help never downloads or fails in CI. The installed check moved into binarymgr and duo reuses it. Wording says Orbit, not Knowledge Graph.

Related Issues

Resolves #8544 (closed) Relates to gitlab-org/orbit/knowledge-graph#1274

How has this been tested?

Unit tests for both help paths, the stale-binary gate, and config read errors. Manual runs against Orbit 0.121.0 below. Reproduced the review cases with a fake managed binary: at 0.100.0 with GITLAB_CI=true, --help and bare glab orbit print glab's text and exit 0. At 0.121.0, help reaches the binary with no prompt, no update check, and no config write. glab duo cli --help diffed identical to main with the binary installed, missing, and in CI.

Screenshots (if appropriate):