Signals back on the accent tint, their icon or initials in orange (#268)

A solid orange tile was too loud. Each Signal's tile is the folder's
accent tint again, and its icon or initials are drawn in the orange of
the Signals icon's point: #ff6a1a in dark. In light it is the light
palette's needle, #c43e00, since signals.svg's #ff5500 on the tint is
about 2:1, too faint for initials (about 3.4:1 instead).

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

docs/signals.md

@@ -20,7 +20,7 @@ their Signals that has not heard about the item yet.
   the set the page's own icons come from: 2,883 icons, solid, regular and brands, searched by name
   and Font Awesome's search terms ("ai" finds the robot). Without one, a Signal shows its initials.
   **Auto** asks Jev to choose (#263), and a Signal made without an icon gets Jev's pick by
-  itself, a moment after it is made. Every Signal's tile is solid in the orange of the folder icon's point.
+  itself, a moment after it is made. Every Signal's tile is in the accent tint the folder had, its icon or initials in the orange of the folder icon's point.
 - **Each Signal's row** says "12 items · 3 unread", as a feed's row counts its own.
 - **The folder's page** lists the Signals, as an OPML's page lists its feeds, with the + for a new one.
 - **A Signal's page** is an ordinary item list: All, Unread, Downloaded and Pinned, search and sort.