webhook through event system, extract data-generators adapter

webhook route now emits WebhookDataReceived event instead of directly
mutating DataProjection and broadcasting. event_handler applies data
and pushes incremental DataUpdate.

clock/static_text generators extracted to data-generators crate behind
DataSourcePort. chrono removed from bootstrap. polling adapters grouped
into Adapters struct.

crates/bootstrap/Cargo.toml

@@ -19,5 +19,4 @@ anyhow.workspace = true
 tracing.workspace = true
 tracing-subscriber.workspace = true
 dotenvy.workspace = true
-chrono.workspace = true
-chrono-tz.workspace = true
+data-generators.workspace = true