Add live dashboard with SSE job events

Expose /jobs, /dedup, and /events routes backed by a new EventBus that
broadcasts job lifecycle and per-job progress over SSE. Serve a static
dashboard from front/ that lists pending and in-progress jobs, streams
agent activity, and shows completed reviews.

Also add migrate-apply/migrate-generate scripts that load .env, update
the Containerfile to ship the front assets and use the apply script, and
refresh the roadmap.

crates/steep-server/Cargo.toml

@@ -7,6 +7,7 @@ edition = "2024"
 reqwest = { workspace = true }
 tokio = { workspace = true }
 tokio-util = { workspace = true }
+tokio-stream = { workspace = true, features = ["sync"] }
 futures-util = { workspace = true }
 serde_json = { workspace = true }
 serde = { workspace = true }