feat: add headless Zoko source checks

Sources/CLI/PlayerCommand.swift

@@ -3,6 +3,7 @@ import Foundation
 enum PlayerCommand {
     case help
     case printDefaultConfig
+    case checkSource(mediaID: String, episode: Int)
     case launch(URL?, newInstance: Bool, noConfig: Bool, progressFile: URL?)
     case launchSource(sourceFile: URL, newInstance: Bool, noConfig: Bool, progressFile: URL?)
     case launchQueue(queueFile: URL, newInstance: Bool, noConfig: Bool)
@@ -15,6 +16,7 @@ enum PlayerCommand {
            terebi --new-instance --source-file PATH [--progress-file PATH]
            terebi --new-instance [--no-config] --queue-file PATH
            terebi --enqueue [--no-config] --queue-file PATH
+           terebi --check-source ZOKO_ANILIST_SUB_URL
            terebi [--new-instance] [--no-config] -- FILE
            terebi --help
            terebi --default-config
@@ -26,6 +28,8 @@ enum PlayerCommand {
       --new-instance Launch a separate player, leaving existing playback untouched.
       --no-config    Use built-in settings instead of config.toml on a fresh launch.
       --url URL      Resolve an HTTP(S) video, Miruro episode or ZokoAnime AniList sub URL.
+      --check-source URL Read-only source/manifest check; one version-1 JSON result,
+                         no player launch, configuration, progress or resume writes.
       --source-file PATH Open a validated resolved HTTP(S) source in a new player.
       --queue-file PATH Open an ordered version-1 stream queue with per-item reports.
       --enqueue      Append a queue to the running player without interrupting playback;
@@ -42,6 +46,16 @@ enum PlayerCommand {
     """
 
     static func parse(_ arguments: [String], directory: URL = URL(fileURLWithPath: FileManager.default.currentDirectoryPath, isDirectory: true)) throws -> PlayerCommand {
+        // Parse this isolated command before any launch flags, paths or file reads.
+        if arguments.prefix(while: { $0 != "--" }).contains("--check-source") {
+            let invalid = ArgumentError("--check-source requires exactly one canonical ZokoAnime AniList sub URL and no other options.")
+            guard arguments.count == 2, arguments[0] == "--check-source",
+                  arguments[1].utf8.count <= 512,
+                  arguments[1] == arguments[1].trimmingCharacters(in: .whitespacesAndNewlines),
+                  let parsed = try? StreamURL.parse(arguments[1]),
+                  case .anilist(let mediaID, let episode) = parsed else { throw invalid }
+            return .checkSource(mediaID: mediaID, episode: episode)
+        }
         var inputs = arguments
         var progressFile: URL?
         var index = 0