PR #13148: the prospects search box searches the loaded leads, and says so

PR #13148 at 0e12584c75. Local dev server against the stage table (read-only), staff session, one company picked. Cropped to the table toolbar, so no rows or names are shown.

Toolbar with a search typed: Searching the 55 loaded leads, 55+ prospects

Before typing, the caption read "Showing the 55 most recently active of 219".
After typing "a", the label reads "Searching the 55 loaded leads", and the window caption is gone because its count describes the unsearched set.
Counted in the browser: 0 list requests after typing, and no whole-window request at any point.
On main, typing switched the page to the whole-window read. The test on main fails on exactly that request.