W-23997997: Remove on-premises from the control-plane compatibility matrix

[kevintroller]

Summary

• Removes On-Premises Runtimes from the Hosting Options control-plane compatibility matrix. That row implied on-premises is a Runtime Manager deploy target of each control plane.
• Clarifies that on-premises Mule does not require a control plane, and that registering the Runtime Manager agent makes the instance Hybrid Standalone.
• Distinguishes on-premises (runtime you host) from Anypoint Platform PCE (control plane you host).

Test plan

• Preview the Hosting Options overview and confirm the matrix has four runtime rows (CH2, CloudHub, RTF, Hybrid).
• Confirm the intro under Control Plane and Runtime Plane Compatibility explains why on-premises is omitted and how it relates to Hybrid.
• Confirm the PCE vs on-premises sentence is accurate and the xref to Run Mule Runtime Engine On-Premises resolves.

[kevintroller]

Superseded by #488, rebased onto latest after Control Planes #487. Closing this PR because the original branch conflicted with hosting-home/modules/ROOT/pages/index.adoc.

Beth’s matrix intro is in #488. The On-Premises row was already removed on latest by #487.