feat(trips): trip settings with a linked journal tab

The Share button becomes the trip's Settings, a round button beside the back
pill. The dialog is rebuilt around three areas (People, Sharing, Journal) with
a side navigation, a fixed height and 960 px width on wide screens.

Journal links one of your journals from the Journey addon to the trip. Every
trip member is ticked as a reader by default, each can be raised to editor or
left out, and the people a save would let in for the first time are named
before it saves. The link can be changed or removed. With a link the trip gets
a Journal tab on desktop and phone that shows the Journey addon's own view,
live through its sync and trip:journal:changed. Nothing shows with the addon
off.

members.shareTrip and nav.share are gone with the button that used them.

client/src/index.css

@@ -824,6 +824,14 @@ input[type="number"], input[type="time"], input[type="date"], input[type="dateti
   :root { --nav-h: calc(64px + env(safe-area-inset-top, 0px)); }
 }
 
+/* A journal shown inside a trip (its Journal tab): the journal's own fixed bars
+   measure themselves from --nav-h, so below the trip's navbar they also have to
+   clear the trip's tab bar. */
+.trip-embedded-journal { --nav-h: 44px; }
+@media (min-width: 768px) {
+  .trip-embedded-journal { --nav-h: calc(64px + env(safe-area-inset-top, 0px) + 44px); }
+}
+
 .dark {
   --bg-primary: #121215;
   --bg-secondary: #1a1a1e;