quak logout ends the session on the server (closes #108)

logout now calls POST /users/logout with the saved token through the new
Client.logoutOnServer(), then deletes session.json even when that call
fails; in that case it says the server session could not be ended and
exits 1. It prints the account's cache directory and says it still holds
decrypted data. The default cache path moves into
defaultCacheDirectory(), shared with Library.open, so both name the same
directory.

Model: opus-5-5

bin/quak.ts

@@ -73,7 +73,7 @@ program
 
 program
     .command("logout")
-    .description("Delete the saved session")
+    .description("End the session on the server and delete the saved session")
     .action(() => run(logoutCommand(context())));
 
 program