Build with Gradle in two modules, and free core of JavaFX

Etappen 1 and 2 of the Compose migration (43 commits).

The Maven build, the single source tree and the JPMS module-info went together.
core now holds the domain and app-desktop the user interface, both built by
Gradle, packaged through jpackage from Gradle, with SpotBugs and PMD wired in.
JavaFX moves to the classpath, which is why the launcher is Main and not the
Application subclass. The PR check, the nightly artifacts, the release and the
AUR packages all build from Gradle; the macOS DMG points at its output.
Verified on Linux, macOS and Windows.

core then loses JavaFX entirely. It observes through kst4contest.observe --
ObservableValue, ObservableRoster, and UiDispatcher as the one boundary a
worker thread crosses to touch the interface. The controller collections become
rosters and the visible station list a pure derivation rather than a
FilteredList/SortedList chain, which is also what fixed two focus defects only
a load test had exposed: the keyboard focus stays where the operator put it,
and the send field keeps it after a row click.

The rule that outlives this commit: ObservableRoster is the store and the list
a view is bound to is a mirror of it, never the other way round.

packaging/aur/kst4contest-git/PKGBUILD

@@ -7,7 +7,7 @@ arch=('x86_64')
 url="https://github.com/praktimarc/kst4contest"
 license=('GPL-3.0-only')
 depends=('gst-plugins-base' 'gst-plugins-good')
-makedepends=('java-environment=21' 'maven' 'git')
+makedepends=('java-environment=21' 'gradle' 'git')
 provides=('kst4contest')
 conflicts=('kst4contest' 'kst4contest-bin')
 source=("kst4contest::git+https://github.com/praktimarc/kst4contest.git")
@@ -15,8 +15,8 @@ sha256sums=('SKIP')
 
 pkgver() {
     cd "${srcdir}/kst4contest"
-    BASE=$(grep -m1 '<version>' pom.xml \
-        | sed 's/.*<version>\(.*\)<\/version>.*/\1/' | sed 's/[-.]nightly//')
+    BASE=$(grep -m1 '^version=' gradle.properties \
+        | cut -d= -f2 | sed 's/[-.]nightly//')
     printf '%s.r%s.g%s' "${BASE}" "$(git rev-list --count HEAD)" "$(git rev-parse --short HEAD)"
 }
 
@@ -26,22 +26,17 @@ build() {
     export JAVA_HOME=$(find /usr/lib/jvm -maxdepth 1 -name 'java-21-*' -type d | head -n 1)
     export PATH="${JAVA_HOME}/bin:${PATH}"
 
-    mvn -B -DskipTests package dependency:copy-dependencies \
-        -DincludeScope=runtime \
-        -DoutputDirectory=target/dist-libs
-
-    cp "$(ls -t target/praktiKST-*.jar | head -n 1)" target/dist-libs/app.jar
+    ./gradlew --offline -S :app-desktop:collectRuntime
 
     mkdir -p dist
-    ADD_MODULES="$(java packaging/AddModules.java)"
+    ADD_MODULES="$(grep -m1 '^jpackageAddModules=' gradle.properties | cut -d= -f2)"
     jpackage \
         --type app-image \
         --name KST4Contest \
         --icon packaging/icons/kst4contest.png \
-        --input target/dist-libs \
+        --input app-desktop/build/dist-libs \
         --main-jar app.jar \
-        --main-class kst4contest.view.Kst4ContestApplication \
-        --module-path target/dist-libs \
+        --main-class kst4contest.view.Main \
         --add-modules "$ADD_MODULES" \
         --dest dist
 }

packaging/aur/kst4contest/PKGBUILD

@@ -7,7 +7,7 @@ arch=('x86_64')
 url="https://github.com/praktimarc/kst4contest"
 license=('GPL-3.0-only')
 depends=('gst-plugins-base' 'gst-plugins-good')
-makedepends=('java-environment=21' 'maven')
+makedepends=('java-environment=21' 'gradle')
 provides=('kst4contest')
 conflicts=('kst4contest-bin' 'kst4contest-git')
 source=("${pkgname}-${pkgver}.tar.gz::https://github.com/praktimarc/kst4contest/archive/refs/tags/v${pkgver}.tar.gz")
@@ -19,17 +19,14 @@ build() {
     export JAVA_HOME=$(find /usr/lib/jvm -maxdepth 1 -name 'java-21-*' -type d | head -n 1)
     export PATH="${JAVA_HOME}/bin:${PATH}"
 
-    mvn -B -DskipTests package dependency:copy-dependencies \
-        -DincludeScope=runtime \
-        -DoutputDirectory=target/dist-libs
-
-    cp "$(ls -t target/praktiKST-*.jar | head -n 1)" target/dist-libs/app.jar
+    ./gradlew --offline -S :app-desktop:collectRuntime
 
     mkdir -p dist
-    # This PKGBUILD builds from a released source tarball, which may predate
-    # packaging/AddModules.java. Older tarballs carry the same list in pom.xml,
-    # which the build keeps in sync with module-info.java from v1.42.0 onwards.
-    if [ -f packaging/AddModules.java ]; then
+    # From the Gradle build onwards the list lives in gradle.properties. Older
+    # tarballs still carry it in pom.xml or derive it via packaging/AddModules.java.
+    if [ -f gradle.properties ]; then
+        ADD_MODULES="$(grep -m1 '^jpackageAddModules=' gradle.properties | cut -d= -f2)"
+    elif [ -f packaging/AddModules.java ]; then
         ADD_MODULES="$(java packaging/AddModules.java)"
     else
         ADD_MODULES="$(sed -n 's:.*<addmodule>\(.*\)</addmodule>.*:\1:p' pom.xml | paste -sd,)"
@@ -45,10 +42,9 @@ build() {
         --type app-image \
         --name KST4Contest \
         "${ICON_ARGS[@]}" \
-        --input target/dist-libs \
+        --input app-desktop/build/dist-libs \
         --main-jar app.jar \
-        --main-class kst4contest.view.Kst4ContestApplication \
-        --module-path target/dist-libs \
+        --main-class kst4contest.view.Main \
         --add-modules "$ADD_MODULES" \
         --dest dist
 }