v0.3.4: one implementation of apply/revert (patch/mw_patch.py)

The "strip the TRUECLOUD_PATCH block" logic existed twice -- in apply.sh's heredoc
and in an inline heredoc in uninstall.sh -- and the uninstall copy was the untested
one. That is precisely how the two could have drifted apart, with apply.sh
reverting one set of files and uninstall.sh another.

Both now call patch/mw_patch.py. 17 new tests cover it, including that
revert_nested never touches restic.py: that file carries a TRUECLOUD_PATCH block
too, but it belongs to the providers module, and removing it would silently break
B2 backups.

apply.sh imports it fail-safe -- on ImportError the backend patch is skipped and
middlewared starts stock, which is this script's whole design principle. The
import uses sys.path.append, never insert(0): prepending would give patch/
precedence over the stdlib for that interpreter, so a future patch/json.py would
shadow the real json module and break the boot.

Also: the README's create_task.py example still taught `--password <secret>`, which
is how a security fix quietly fails to land. It now shows --password-stdin.

132 tests, ruff and shellcheck clean.

README.md

@@ -376,18 +376,25 @@ host address or API key:
 # List your cloud credentials to find the right ID
 python3 /mnt/tank/truenas-truecloud-patch/patch/create_task.py list-credentials
 
-# Create a task with a B2 credential (id=3)
+# Create a task with a B2 credential (id=3).
+# The restic repo password is read from stdin, so it never lands in your shell
+# history — nor in any process's argv, where `ps` would expose it.
+printf '%s' 'restic-repo-password' | \
 python3 /mnt/tank/truenas-truecloud-patch/patch/create_task.py create \
     --name "tank-to-b2" \
     --path /mnt/tank/data \
     --credential 3 \
     --bucket my-bucket \
     --folder backups/tank \
-    --password "restic-repo-password" \
+    --password-stdin \
     --cache-path /mnt/tank/.restic-cache \
     --keep-last 14
 ```
 
+Omit `--password-stdin` and you'll be prompted for the password instead. `--password
+<secret>` still works but warns: that password is the encryption key for the whole
+repository, and a CLI argument persists in your shell history forever.
+
 > **Always pass `--cache-path`.** Without it TrueNAS runs restic with `--no-cache`,
 > which re-fetches all repo metadata from the provider every run — glacially slow
 > on large repos. Point it at a writable dir on a pool with free space.