feat(daemon): make every window a view of one shared session

Two TUIs on one daemon behaved as two separate windows that happened to share
a login: each showed only the transfers it had queued and the searches it had
run, and neither said it was attached to anything.

The status bar now names the daemon, and both lists are views of the session:
transfers and searches appear in every window, dismissing one dismisses it
everywhere, and a window opened later starts from what is already running
rather than blank. message read likewise starts from the conversation the
daemon collected instead of only what arrives while it runs.

Search state needed the daemon to say when a query went out. The window a
search collects for belongs to whichever client started it, so without that
every other window showed a running search as finished the moment it appeared
— which is what it did. The summary carries a file count too, so a window has
the right number before it has pulled the results across.

Adds Client::forget_search, which the library had no way to do: a resident
client otherwise holds every result set it has ever seen, and a window that
dismissed a search had no way to say so.

A review of the first cut found five defects, all fixed here and all covered:
syncing ran locally too, where it cost a full copy of every result set per
frame and deleted the completed-download history restored from disk; a
transfer could be listed twice by racing its own registration; clearing all
searches did not reach the session, so every row came back; a search dismissed
elsewhere never left; and a wishlist search reported as finished the instant
it went out.

website/src/pages/docs.tsx

@@ -250,6 +250,12 @@ const Daemon = () => (
           open, so there is no address to pass and no token to handle. Without one
           running, everything behaves exactly as it did before.
         </p>
+        <p>
+          Every window is a view of the same session. Open a second TUI and it shows the
+          searches and transfers already running; queue something in either and both see
+          it. The status bar names the daemon, and closing a window leaves its downloads
+          going, because they belong to the daemon rather than the window.
+        </p>
         <p>
           Why bother: the server permits a single session per account. Two one-off
           commands at once either cut each other off, or push you into a throwaway