An expired session exits 3 with one line saying to run quak login (closes #164)

A 401 from the server that ends a command reaches run in src/cli-run.ts as
an ApiError; run prints one line saying to run "quak login" and exits 3.
quak backup meets it on its first refresh, before it touches any file. For
the commands that load the saved session, a missing or corrupt session file
keeps its message and also exits 3.

Judgement call: quak logout is unchanged; it handles its own errors and
deletes the session file whatever the server answers.
Judgement call: quak backup still prints its two progress lines before the
error line.

Model: opus-5-5

TODO.md

@@ -25,14 +25,15 @@ declares one.
 
 # Completed Steps
 
-- 2026-10-06: When the refresh a command starts with gets HTTP 401, because the
+- 2026-10-06: When the server answers HTTP 401 and that ends a command that
-  server no longer accepts the saved session's token, the command prints one
+  loads the saved session, because the server no longer accepts its token, the
-  line, `quak: the saved session is no longer valid; run "quak login"`, and
+  command prints one line,
-  exits 3 (issue 164). A missing or corrupt session file keeps its message and
+  `quak: the saved session is no longer valid; run "quak login"`, and exits 3
-  now also exits 3, so a cron job can tell that the user must log in again.
+  (issue 164). `quak backup` meets that 401 on the refresh it starts with,
-  `run` in `src/cli-run.ts` recognises the 401, which reaches it unchanged from
+  before it touches any file. For the same commands, a missing or corrupt
-  the refresh, so `quak backup` stops there before it touches any file. Every
+  session file keeps its message and also exits 3, so a cron job can tell that
-  other error still exits 1.
+  the user must log in again. `quak logout` is unchanged. `run` in
+  `src/cli-run.ts` recognises the 401, which reaches it unchanged.
 
 - 2026-10-06: `quak backup` writes the account and album records
   `backup-metadata` writes (issue 166): `account.json` with the account's