Draw the whole interface in Compose

Etappen 3 to 6a of the migration (129 commits). Every window the operator sees
is Compose; the JavaFX ones still exist beside them so the two could be
compared against a live session, which is the only way the differences came to
light.

The toolchain first, then the settings window with its eleven tabs and 72 real
preferences; then the multi-column table as a component, and with it the rules
it needs -- stable row identity, a selection that survives a refresh, column
order the operator can drag, and a repaint when the rows change rather than
when the list instance does. Then the update and monitor windows, and the main
window: 22 station columns, the filter bar, the selected-station panel, the
message tabs, the priority bar, the sked controls, the status indicators and
the timeline, assembled behind a splitter because Compose has none.

The map stops being a WebView. A Compose canvas projects WebMercator tiles
itself, with the clustering in core and an asynchronous fetcher in place of the
local tile proxy; derive() becomes a pure Kotlin reimplementation instead of a
reflection call into com.sun.javafx.

Most of the volume here is parity the operator would notice rather than new
behaviour: desktop density instead of Material's phone minimums, colours taken
from the JavaFX stylesheets instead of Material's palette, row dividers, band
columns, grid-square labels and their colours, the home marker and antenna
beam, pinch-to-zoom under Wayland, and layouts that survive a window narrower
than the chart they stack.

Two lessons are worth more than the diff. A control bound to a value Compose
cannot observe writes through and never redraws -- that one shipped repeatedly
with a green build, because no test drew anything. And a layout that clips
instead of wrapping is worse than one that is merely too narrow: half a word
is the worst available outcome.

gradle/libs.versions.toml

@@ -7,6 +7,8 @@ junit = "5.10.1"
 mockito = "5.7.0"
 mockitoCompile = "5.17.0"
 jetbrainsAnnotations = "24.0.1"
+kotlin = "2.2.0"
+composeMultiplatform = "1.8.2"
 spotbugsPlugin = "6.0.26"
 spotbugs = "4.9.8"
 pmd = "7.17.0"
@@ -24,4 +26,7 @@ junit-platform-launcher = { module = "org.junit.platform:junit-platform-launcher
 
 [plugins]
 javafx = { id = "org.openjfx.javafxplugin", version.ref = "javafxPlugin" }
+kotlinJvm = { id = "org.jetbrains.kotlin.jvm", version.ref = "kotlin" }
+composeCompiler = { id = "org.jetbrains.kotlin.plugin.compose", version.ref = "kotlin" }
+composeMultiplatform = { id = "org.jetbrains.compose", version.ref = "composeMultiplatform" }
 spotbugs = { id = "com.github.spotbugs", version.ref = "spotbugsPlugin" }