Files: a press on a download's button stays with the button

gpui runs the click of every pressed element under the pointer, so a
press on a finished download's Show button also opened the file through
the pressable row. The actions' box stops the press on mouse down, so
the row starts no click of its own.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

TASKS.md

@@ -327,3 +327,4 @@ Per-component lines live in `tasks/`. Tags there:
 | T27b | 2 | PASS | |
 | T27c | 1 | FAIL | recent and found files were keyed by their place, so the cursor left a file an open moved |
 | T27c | 2 | PASS | |
+| T27d | 1 | FAIL | a press on a finished download's Show button also opened the file through its row |