Support isolated live window ScreenCast streams

Render selected toplevels through a private portal-only capture protocol, preserve logical snapshot geometry, and renegotiate PipeWire video on window resizing. Bound outstanding snapshots and retry temporary contention; stop on source closure and session locking.

Validation: portal unit tests (31), capture budget unit, private-bus portal contracts, and real nested/PipeWire isolation, workspace, resize, close and paused-lock tests pass. Independent review cleared. Monitor restore integration timed out on both this build and the unchanged previous compositor under the current nested host.

portal/Cargo.toml

@@ -14,6 +14,7 @@ name = "ferese-record"
 path = "src/record_main.rs"
 
 [dependencies]
+ferese-protocols = { path = "../crates/ferese-protocols", default-features = false, features = ["client"] }
 ferese-ipc = { path = "../crates/ferese-ipc" }
 url = "2.5"
 png = "0.18"