Test quak backup end to end against a fake Ente server (closes #186)

test/cli/backup-end-to-end.test.ts runs backupCommand through run, as
bin/quak.ts does, with the real loadSession reading a session saved after
logging in, and every request answered by a fake of the Ente HTTP API serving
data encrypted with libsodium. It covers the backup tree of an account with
two albums of its own and one shared with it, a second run that downloads
nothing, a download that succeeds after two 503s, a 404 recorded in
failures.json with exit 1, a refresh answered 401 with exit 3, and --verify
putting back an original changed on disk.

The fake server and the account it logs in moved from the backup-metadata
test into test/ente-server.ts, unchanged, so both tests use them.

Model: opus-5-5

TODO.md

@@ -25,6 +25,17 @@ declares one.
 
 # Completed Steps
 
+- 2026-10-14: `test/cli/backup-end-to-end.test.ts` runs `quak backup` as cron
+  does (issue 186): `backupCommand` and `run`, the real `loadSession` reading a
+  session saved after logging in, and every request answered by a fake of the
+  Ente HTTP API serving data encrypted with libsodium. It covers the backup tree
+  of an account with two albums of its own and one shared with it, a second run
+  that downloads nothing, a download that succeeds after two 503s, a 404 that
+  lands in `failures.json` with exit 1, a refresh answered 401 with exit 3, and
+  `--verify` putting back an original changed on disk. The fake server and the
+  account it logs in moved from the backup-metadata test into
+  `test/ente-server.ts`, unchanged.
+
 - 2026-10-14: `files --collection`, `get`, `get-thumb` and
   `helper fix-missing-thumbnails --file` take an ID only when it is written in
   decimal digits and is a safe integer (issue 185). Before, `Number()` read