Add control repo guidance to post-install trail

[miharp]

Problem

Following the new-user install trail — Install OpenVox Server → Install OpenVox agent on Linux — leaves the reader with a running server and enrolled agents but no guidance on what to do with them.

The install_linux.markdown page has no "What to do next" section. Control repo setup is the natural next step but is completely absent from the trail.

Suggestion

• Add a "What to do next" section to docs/_openvox_8x/install_linux.markdown that points toward control repo setup
• Add or link a control repo getting-started page that covers the basics: r10k/Code Manager, a minimal repo structure, and how to point the server at it