feat(client/windows): per-host clipboard toggle

The bridge landed always-on whenever the host permitted it; sharing a
clipboard is a trust decision about a specific host, so it needs to be
opted into. Mirrors the Apple client's per-host model
(StoredHost.clipboardSync, "Share clipboard with this host") rather than a
global switch: KnownHost::clipboard_sync, toggled from the host card's
overflow menu, default off.

The session binary resolves the stored flag itself in session_params, so a
direct connect and the console's own launches honor the same decision
without every caller having to remember to pass it.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

clients/windows/src/app/pair.rs

@@ -59,6 +59,7 @@ pub(crate) fn pair_page(props: &Svc, cx: &mut RenderCx) -> Element {
                                 paired: true,
                                 last_used: None,
                                 mac: target3.mac.clone(),
+                                clipboard_sync: false,
                             });
                             let _ = k.save();
                             connect(&ctx3, &target3, Some(fp), &ss, &st);