Keep a feed out of Signals, and a feed's settings in named parts (#289, #290)

hide_from_signals on a subscription, on an OPML or creator covering every
show in it, as hide_from_all does for All Subscriptions: the judge does
not put its items to Jev, and each Signal's list and counts leave them
out. shown_in() is the one SQL rule for both.

The settings dialog had grown one captioned setting at a time into a
single column, one part boxed and the rest not. It is in named parts now,
the name in a column beside the controls and above them on a phone, ruled
apart; All Subscriptions and Signals carry the sidebar's icons. The
address, the same for everyone, moves to the foot.

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

web/src/types.ts

@@ -39,6 +39,8 @@ interface Feed {
   kept: boolean;
   /** Left out of All Subscriptions by its own setting; a show is also when its OPML is (#288). */
   hide_from_all: boolean;
+  /** The same for Signals (#289). */
+  hide_from_signals: boolean;
   private: boolean;
   private_by_address: boolean;
 }