fix: tag counts, chip focus, upload naming, share links and unsized clips hold after round 2

- A tag counts the followed channels the Subscriptions tab shows: hidden ones are left out, and a
  subscribe, unsubscribe, hide or tag toggle refreshes the count. The Tag manager's row and its
  hover list count the same channels as the chip; /api/tags sends both counts under their names.
- A chip's count keeps the chip's colour after a dot (a dimmed count fell under 4.5:1). A pick in
  the open "+N" fold closes it; a chip that leaves the list hands the focus to the one in its place.
  The fold is a dialog of toggle buttons, not an empty menu.
- Upload: a folder name left by a press is made once the press is over, if the dialog is still
  open, instead of guessing a dismissal from Modal's markup. While the folder is made, its place
  holds the focus and a live region says so.
- Share: an expired link has no Copy and a warn badge; the link made on open goes into the cached
  list, so a reopen makes no second one; the New link form survives the link made on open.
- Watch: a repeated Enter sends one unlock while one is on its way. See all buttons are named with
  their rail.
- An unsized clip of a rotated file gets the upright size its crop cut.

backend/app/downloads/edit.py

@@ -89,9 +89,10 @@ def crop_filter(crop: dict) -> str:
 
 
 def crop_stored_size(crop: dict, src_w: int | None, src_h: int | None) -> tuple[int, int] | None:
-    """The stored size `crop_filter` cuts out of a `src_w` x `src_h` file, evened as `EVEN_FRAME`
-    evens it — the clip's size when ffprobe cannot tell. A crop counted in the shown picture is a
-    fraction of the file's frame, not its own pixel count; None when the source size is unknown."""
+    """The size `crop_filter` cuts out of a `src_w` x `src_h` frame, evened as `EVEN_FRAME` evens it —
+    the clip's size when ffprobe cannot tell. The frame is the one ffmpeg's filters see: a rotated
+    file's stood upright, its stored size turned (the caller's to turn). A crop counted in the shown
+    picture is a fraction of that frame, not its own pixel count; None when the size is unknown."""
     if crop.get("frame_w") and crop.get("frame_h"):
         if not src_w or not src_h:
             return None