feat(tui): search a room's log and members, and a conversation

A busy room's log scrolls past and its member list runs to a thousand
names, with nothing to narrow either. In a room / now filters the log
to lines mentioning the text and u filters the member list, the same
way the room list and the results filter: type, Enter keeps it, Esc
clears it before it leaves the room. The inbox takes / over the open
conversation. The member keys, b and m among them, act on the narrowed
list, and the titles say what is filtered and how many made it.

website/src/pages/docs.tsx

@@ -47,6 +47,8 @@ const ROOM_KEYS: readonly (readonly [string, string])[] = [
   ['x', 'leave the active room'],
   ['l', 'back to the room list'],
   ['↑ ↓', 'select a member'],
+  ['/', 'search the chat log; in the inbox, the conversation'],
+  ['u', 'filter the member list'],
   ['b', "browse the member's files"],
   ['m', 'message the member'],
 ]