fix: enable KCEF support in Docker and fix init race condition

Add KCEF build args to docker-compose.yml so the image is built with
Xvfb and CEF binaries, enabling WebView-based sources like MangaFire.

Remove redundant kcefDir.createDirectories() in ServerSetup which caused
FileAlreadyExistsException when KCEF.init tried to create the same dir.

server/src/main/kotlin/suwayomi/tachidesk/server/ServerSetup.kt

@@ -548,7 +548,6 @@ fun applicationSetup() {
                 )
 
                 val kcefDir = Path(applicationDirs.dataRoot) / "bin/kcef"
-                kcefDir.createDirectories()
                 installDir(kcefDir.toFile())
             },
             onError = { it?.printStackTrace() },