Fix kill switch not cleared on reinstall; guard midclt delete; tighten sitecustomize imports

install.sh: running install.sh after a recover.sh left /data/truecloud-patch/disabled
in place, so apply.sh silently skipped all patching and middlewared restarted
without the patch. Clear the kill switch file before running apply.sh.

uninstall.sh: midclt initshutdownscript.delete was unguarded under set -euo pipefail,
so a delete failure (already-removed entry, transient API error) aborted the script
before sitecustomize.py was cleaned up or /data/truecloud-patch/ was removed. Now
guarded with an if/else that warns and continues.

sitecustomize.py: move importlib.machinery/.util imports inside the if block in
find_spec so they only execute when intercepting our two target modules, not on
every module import across the whole process. In _install(), import os before
importlib.util so the kill switch check (cheap) runs before the importlib import
(slightly heavier on first use). Remove the unused orig variable in _patch_restic.

patch_ui.py: add explicit encoding="utf-8" to both open() calls. errors="replace"
on read so malformed bytes in a bundle don't silently skip a candidate file.

patch/patch_ui.py

@@ -60,7 +60,7 @@ def find_bundle(webui):
                 continue
             path = os.path.join(root, name)
             try:
-                with open(path) as fh:
+                with open(path, encoding="utf-8", errors="replace") as fh:
                     content = fh.read()
                 if FIND.search(content):
                     matches.append((path, content))
@@ -112,7 +112,7 @@ def main():
     patched, count = FIND.subn(REPLACE, content)
 
     try:
-        with open(path, "w") as fh:
+        with open(path, "w", encoding="utf-8") as fh:
             fh.write(patched)
     except OSError as exc:
         print(f"[truecloud-patch] ERROR: Could not write {path}: {exc}")