Fix five quality findings from second re-review

sitecustomize.py: when find_spec resolves real_spec as None (module absent
after a TrueNAS update), record a FAIL status and mark the module done so
hook_status.json is still written and cmd_verify shows a diagnostic FAIL
instead of the ambiguous "no status file found".

sitecustomize.py: the AttributeError fallback in the URL-fix wrapper now
writes a WARNING to stderr before returning the unmodified result, making
the unexpected ResticConfig type visible in journalctl.

apply.sh: after falling back to bare python3, verify that python3 can also
import middlewared; if not, emit a second warning so the operator knows the
backend patch may be installed in the wrong site-packages directory.

patch_ui.py: abort (return without writing) when FIND.subn produces a count
other than 1, instead of committing a doubly-patched bundle and having
subsequent runs silently accept it via the MARKER check.

uninstall.sh: when a vendor sitecustomize.py backup exists, use mv to
atomically overwrite our file rather than rm-then-mv; eliminates the window
where a read-only /usr causes rm to fail under set -e, aborting before the
backup is restored.

patch/create_task.py

@@ -114,7 +114,7 @@ def cmd_verify():
 
     print()
     if all_ok:
-        print("All patches active. B2 and S3 backups should work.")
+        print("All patches installed. Run a test backup to confirm end-to-end.")
     else:
         print("One or more patches failed to apply.")
         print("Check /data/truecloud-patch/apply.log and journalctl -u middlewared")