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.

recover.sh

@@ -17,7 +17,7 @@
 #   bash /mnt/tank/truenas-truecloud-patch/patch/apply.sh
 #   systemctl restart middlewared
 
-VERSION="0.3.3"
+VERSION="0.3.4"
 
 PATCH_DIR="$(cd "$(dirname "$0")" && pwd)"