Emit bread.paper.changed after a successful set

Link bread-utils v0.7.1 (bread-client) and publish
{ "path": "<wallpaper>" } once awww + wal + bread-theme reload
all succeed. Silent no-op if breadd is down. breadpaper is
CLI-only — no watch subscriber; modules should bread.exec
("breadpaper set …"). See EVENTS.md.

Cargo.toml

@@ -8,3 +8,5 @@ license = "MIT"
 [dependencies]
 clap = { version = "4", features = ["derive"] }
 anyhow = "1"
+serde_json = "1"
+bread-utils = { git = "https://git.breadway.dev/Breadway/bread-ecosystem", tag = "v0.7.1", features = ["bread-client"] }