chore: enforce missing_docs from the workspace manifest

One [workspace.lints.rust] table replaces the deny attribute
scattered across every lib.rs, and each crate opts in through
[lints]. The lint now also reaches the integration-test crates,
whose roots gain their one-line docs.

integrations/rhema-forge-integration/Cargo.toml

@@ -26,3 +26,6 @@ reqwest = { version = "0.12", features = ["json"] }
 tokio = { workspace = true, features = ["rt-multi-thread", "macros", "sync", "time"] }
 # In-process HTTP mocks for offline tests
 wiremock = "0.6"
+
+[lints]
+workspace = true