[tony]

Closes #126

Part of libtmux/docs#231

The Kotlin Server KDoc and the Scala Server Scaladoc now have the shape the docs site draws as a capability directory (groupDirectory), as the Java Server page already does: eight groups in each, a bold-led paragraph of guidance followed by a paragraph that holds only references. Until now each group mixed guidance and references in one paragraph, so libtmux.org rendered Kotlin and Scala as prose.

• The introduction, the group titles and the guidance of every group are kept word for word, because the sentences tell members apart by name.
• Each group's guidance is followed by one paragraph of the members it covers, as the KDoc [name] and [label][target] references and the Scaladoc [[name]] references the comments already used; types stay in the guidance only.
• The closing paragraph about cmd, run, batch, chain and asJava (Kotlin) and cmd, run, batch and chain (Scala) is now its own group, "Running a command".
• One commit per facade. Session already draws a directory on the Java side, and the Kotlin and Scala Session, Window and Pane comments have no grouped sections, so the issue's last bullet has nothing more to restructure.

The site does not read KDoc's [label][target] or Scaladoc's [[name]] references in the directory yet; libtmux/docs#231 adds them ([name] is already read). Until that lands the sections read as ordinary Markdown, which Dokka and Scaladoc render as before.

Checked:

• ./gradlew :libtmux-scala:scaladocSite :libtmux-kotlin:dokkaGeneratePublicationHtml succeeds; the scaladoc task fails on an unresolved link and its two warnings are in Observation.scala, and Dokka links exactly the references it linked before the change
• every reference of the old groups is still in the new ones, in both files
• the docs-side parser work for Recognize every port's link syntax in the capability directory docs#231 draws eight rows for each new text and none for the old ones