refactor(scraper): implement graceful shutdown with broadcast channels

Replace task abortion with broadcast-based graceful shutdown for scheduler and workers. Implement cancellation tokens for in-progress work with 5s timeout. Add tokio-util dependency for CancellationToken support. Update ServiceManager to use completion channels and abort handles for better service lifecycle control.

Cargo.toml

@@ -36,6 +36,7 @@ sqlx = { version = "0.8.6", features = [
 thiserror = "2.0.16"
 time = "0.3.43"
 tokio = { version = "1.47.1", features = ["full"] }
+tokio-util = "0.7"
 tl = "0.7.8"
 tracing = "0.1.41"
 tracing-subscriber = { version = "0.3.20", features = ["env-filter", "json"] }