Phase 5a: add configurable Jai module roots

src/main/kotlin/dev/hgh/jai/settings/JaiAdditionalLibraryRootsProvider.kt

@@ -0,0 +1,17 @@
+package dev.hgh.jai.settings
+
+import com.intellij.openapi.project.Project
+import com.intellij.openapi.roots.AdditionalLibraryRootsProvider
+import com.intellij.openapi.roots.SyntheticLibrary
+import com.intellij.openapi.vfs.VirtualFile
+
+/** Makes configured external Jai directories part of IntelliJ's indexed library scope. */
+class JaiAdditionalLibraryRootsProvider : AdditionalLibraryRootsProvider() {
+    override fun getAdditionalProjectLibraries(project: Project): Collection<SyntheticLibrary> {
+        val roots = JaiProjectSettings.getInstance(project).configuredRoots()
+        if (roots.isEmpty()) return emptyList()
+        return listOf(SyntheticLibrary.newImmutableLibrary(roots))
+    }
+
+    override fun getRootsToWatch(project: Project): Collection<VirtualFile> = JaiProjectSettings.getInstance(project).configuredRoots()
+}