share the forge and schedule wire types through swarm-controller-api

swarmctl hand-mirrored the controller's forge make-admin response and
the /api/schedules bodies. Both now import them from a new serde-only
crate, swarm-controller-api, the way hivectl and hive-c0re share
hive-host-sock. ToSchema sits behind its schema feature, which only
the controller turns on.

The wire format is unchanged: round-trip tests in the new crate pin
each type against the JSON the controller and swarmctl produced, and
the controller's OpenAPI document for these routes is byte-identical.

Files: swarm-controller-api/ is the new crate; swarm-controller and
swarmctl (src, Cargo.toml, Cargo.lock, root Cargo.toml) switch to it;
CLAUDE.md lists the crate and which swarmctl shapes are still local
mirrors; swarmctl/README.md says the forge and schedule bodies come
from the crate, so none of its lines still call them mirrored.

Part of #5472.

swarm-controller-api/src/forge.rs

@@ -0,0 +1,42 @@
+//! `POST /api/forge/users/{name}/admin`.
+
+use serde::{Deserialize, Serialize};
+
+/// What `POST /api/forge/users/{name}/admin` found.
+#[derive(Clone, Copy, Debug, PartialEq, Eq, Serialize, Deserialize)]
+#[cfg_attr(feature = "schema", derive(utoipa::ToSchema))]
+#[serde(rename_all = "snake_case")]
+pub enum ForgeAdminChange {
+    Promoted,
+    AlreadyAdmin,
+}
+
+/// Success body of `POST /api/forge/users/{name}/admin`.
+#[derive(Debug, PartialEq, Eq, Serialize, Deserialize)]
+#[cfg_attr(feature = "schema", derive(utoipa::ToSchema))]
+pub struct MakeForgeAdminResponse {
+    pub change: ForgeAdminChange,
+}
+
+#[cfg(test)]
+mod tests {
+    use super::{ForgeAdminChange, MakeForgeAdminResponse};
+
+    #[test]
+    fn both_changes_round_trip() {
+        for (change, wire) in [
+            (ForgeAdminChange::Promoted, r#"{"change":"promoted"}"#),
+            (
+                ForgeAdminChange::AlreadyAdmin,
+                r#"{"change":"already_admin"}"#,
+            ),
+        ] {
+            let resp = MakeForgeAdminResponse { change };
+            assert_eq!(serde_json::to_string(&resp).unwrap(), wire);
+            assert_eq!(
+                serde_json::from_str::<MakeForgeAdminResponse>(wire).unwrap(),
+                resp
+            );
+        }
+    }
+}