fix: share, upload, crop, auto-skip, tag chips and See all hold what they claim

- Share: a link that expired is never copied (the dialog and one-click Share pick a live one,
  else make one), says it expired, and the copy-on-open claim clears on the next copy.
- A password-protected file link asks to open a file, not to watch a video.
- Upload: Cancel, the close button or the backdrop while naming a folder makes no folder; a failed
  refetch keeps the target; a folder being made says so.
- Crop: an infinite number is dropped, not a 500; an unprobed clip's size follows a shown-size crop;
  the edit_spec docs name frame_w/frame_h; the join and rotated paths are tested.
- Auto-skip: the wait gives way on a marker too short for it, so the skip still fires.
- Tag chips count the followed channels (subscribed_count) and a toggled chip keeps the focus.
- Continue watching's See all sorts by last watched when in progress was already on.

backend/tests/test_folder_links.py

@@ -150,6 +150,7 @@ def test_a_password_folder_link_shows_nothing_until_unlocked(shelf, client):
     assert client.get(f"/api/public/watch/{token}").json() == {
         "needs_password": True,
         "kind": "folder",
+        "video": False,
     }
     bare = f"/api/public/watch/{token}/files/{shelf['inside'][0]}/file"
     assert client.get(bare).status_code == 403
@@ -312,7 +313,7 @@ def test_a_password_file_link_says_it_opens_a_file(shelf, client):
         .json()
     )
     meta = client.get(f"/api/public/watch/{made['token']}").json()
-    assert meta == {"needs_password": True, "kind": "file"}
+    assert meta == {"needs_password": True, "kind": "file", "video": True}
 
 
 def test_a_file_whose_bytes_are_gone_is_not_offered(shelf, client, db):