userpage: generate & display referral links

shown on a new card, with an explanation, the number of remaining uses,
and expiry of the current referral.

lang/form/en-us.json

@@ -34,7 +34,9 @@
         "resetPasswordThroughLink": "To reset your password, enter your username, email address or a linked contact method username, and submit. A link will be sent to reset your password.",
         "resetSent": "Reset Sent.",
         "resetSentDescription": "If an account with the given username/contact method exists, a password reset link has been sent via all contact methods available. The code will expire in 30 minutes.",
-        "changePassword": "Change Password"
+        "changePassword": "Change Password",
+        "referralsDescription": "Invite friends & family to Jellyfin with this link. Come back here for a new one if it expires.",
+        "copyReferral": "Copy Link"
     },
     "notifications": {
         "errorUserExists": "User already exists.",
@@ -76,4 +78,4 @@
             "plural": "Must have at least {n} special characters"
         }
     }
-}
+}