Add playlist permission management commands

Introduces a new 'permission' command to grant or revoke read, write, or remove permissions for playlists. Refactors playlist access checks to support granular permissions and shared playlist operations, and updates localized messages for permission actions.

langs/EN.json

@@ -205,6 +205,15 @@
         "inbox": {
             "full": "Sorry! {0}'s inbox is full.",
             "noMessages": "There are no messages in your inbox."
+        },
+        "permissions": {
+            "granted": "Granted **{1}** permission to {0} for playlist [`{2}`].",
+            "revoked": "Revoked **{1}** permission from {0} for playlist [`{2}`].",
+            "alreadyGranted": "{0} already has **{1}** permission for this playlist.",
+            "notGranted": "{0} does not have **{1}** permission for this playlist.",
+            "cannotModifySelf": "You cannot modify your own permissions.",
+            "invalidPermission": "Invalid permission type. Must be: read, write, or remove.",
+            "invalidAction": "Invalid action. Must be: grant or revoke."
         }
     },
     "search": {