Add native file picker to core test UI

shared/src/jvmMain/kotlin/com/vnidrop/app/core/FilePicker.jvm.kt

@@ -0,0 +1,39 @@
+package com.vnidrop.app.core
+
+import androidx.compose.runtime.Composable
+import androidx.compose.runtime.remember
+import java.awt.FileDialog
+import java.awt.Frame
+import java.io.File
+
+@Composable
+actual fun rememberShareFilePicker(
+	onFilePicked: (PickedShareFile) -> Unit,
+	onError: (String) -> Unit,
+): ShareFilePicker = remember(onFilePicked, onError) {
+	object : ShareFilePicker {
+		override fun pickFile() {
+			try {
+				val dialog = FileDialog(null as Frame?, "Select file to share", FileDialog.LOAD)
+				dialog.isVisible = true
+				val directory = dialog.directory
+				val file = dialog.file
+				if (directory != null && file != null) {
+					val selected = File(directory, file)
+					onFilePicked(PickedShareFile(selected.absolutePath, selected.name))
+				}
+			} catch (error: Throwable) {
+				onError(error.message ?: error.toString())
+			}
+		}
+	}
+}
+
+actual suspend fun sharePickedFile(
+	repository: CoreRepository,
+	file: PickedShareFile,
+	transferName: String,
+	senderName: String,
+) {
+	repository.sharePath(file.value, transferName, senderName)
+}