fix(images): background jobs skip files hidden by the removal mark; walkers skip trash folders inside output roots (#501)

- Thumbnail jobs and the legacy scan_output_dir listing leave
  library-removed files out (one mark check, mark_hides).
- Missing-file links also forgets removal marks that hide nothing any
  more (file gone from a folder that exists, or changed), only under a
  readable, non-empty source, re-checked at apply.
- The sidebar Images, Favorites and Needs review counts and the
  collection counts are read again when an image_delete job ends.
- utils/media_folders.py: one skip for thumbnails and trash folders
  (.Trash, .Trash-<uid>, .Trashes, $RECYCLE.BIN) used by every walker,
  the image monitor and the delete review.

database/image_removal.py

@@ -144,6 +144,23 @@ def removed_from_library(conn, path) -> bool:
     return False
 
 
+def mark_hides(marks: dict, locator: str, path) -> bool:
+    """Whether a removal mark in *marks* hides the file at *path* (blocking).
+
+    *marks* is ``{locator: (size, mtime_ns)}``. The mark of *locator* hides
+    the file while ``os.lstat(path)`` still has the size and ``mtime_ns`` it
+    was removed with; a file that cannot be looked at is not hidden.
+    """
+    mark = marks.get(locator)
+    if mark is None:
+        return False
+    try:
+        info = os.lstat(path)
+    except OSError:
+        return False
+    return (info.st_size, info.st_mtime_ns) == tuple(mark)
+
+
 def write_mark(conn, locator, size, mtime_ns):
     _write_mark(conn, locator, size, mtime_ns, utc_now_iso())