Fix six quality findings from iterative code review

- patch_ui.py: find_bundle now matches MARKER so already-patched files
  return early and print 'UI already patched' instead of the misleading
  'filterByProviders pattern not found' warning
- install.sh: scope warning grep to current run only (record log offset
  before apply.sh, tail -c +N to read only new bytes)
- install.sh: fix misleading 'before continuing' wording on warning banner
- install.sh: fix grep anchor (^WARNING: missed [truecloud-patch] WARNING: lines)
- uninstall.sh: add import-middlewared verification after Python detection,
  matching apply.sh fallback logic

patch/patch_ui.py

@@ -58,7 +58,7 @@ def find_bundle():
             try:
                 with open(path, encoding="utf-8", errors="replace") as fh:
                     content = fh.read()
-                if FIND.search(content):
+                if FIND.search(content) or MARKER in content:
                     return webui, path, content
             except OSError:
                 continue