feat(club): ownership-backed squad manager assignment

Add a generic, durable squad->manager assignment (migration 0023
squad_managers) so a manager persists across squad save, reload, and
server restart, backed by authoritative Core owned_cards.

- squad_managers(squad_id PK, owned_card_id, updated_at) with ON DELETE
  CASCADE on both FKs: quick-selling the manager auto-clears the
  assignment (no resurrection); one manager per squad (no duplicates).
- club::{get,set,clear}_squad_manager validate club ownership of both the
  squad and the card, and re-check ownership on read (defends against a
  stale row left by a market transfer).
- GET/PUT /club/manager routes expose the assignment; FIFA wire meaning
  stays in the adapter.

Tests: persistence across reload+restart (headline), reassignment
replace/no-duplicate, clear/no-resurrection, cascade on quick-sell,
foreign-card rejection.

src/routes/club.rs

@@ -124,3 +124,42 @@ pub async fn get_milestones(State(state): State<AppState>, game: GameId) -> AppR
         "club_level": club.level,
     })))
 }
+
+/// The owned card assigned as the active squad's manager, or `null`. Generic:
+/// Core returns the ownership-backed assignment; the FIFA 17 adapter shapes the
+/// manager wire item from it (itemType/contract/chemistry are adapter concerns).
+pub async fn get_squad_manager(
+    State(state): State<AppState>,
+    game: GameId,
+) -> AppResult<Json<Value>> {
+    let profile = profile_svc::get_active_profile(&state.pool, game.as_str()).await?;
+    let club = club_svc::get_club_by_profile(&state.pool, &profile.id).await?;
+    let manager = club_svc::get_squad_manager(&state.pool, &club.id).await?;
+    Ok(Json(json!({ "manager": manager })))
+}
+
+#[derive(Deserialize)]
+pub struct SetManagerRequest {
+    /// The owned card to assign as manager, or `null`/absent to clear it.
+    pub owned_card_id: Option<String>,
+}
+
+/// Assign (or, with a null/absent `owned_card_id`, clear) the active squad's
+/// manager. Fail-closed: the card must be owned by this club and the club must
+/// have a squad. Returns the resulting assignment.
+pub async fn put_squad_manager(
+    State(state): State<AppState>,
+    game: GameId,
+    Json(req): Json<SetManagerRequest>,
+) -> AppResult<Json<Value>> {
+    let profile = profile_svc::get_active_profile(&state.pool, game.as_str()).await?;
+    let club = club_svc::get_club_by_profile(&state.pool, &profile.id).await?;
+    match req.owned_card_id {
+        Some(owned_card_id) => {
+            club_svc::set_squad_manager(&state.pool, &club.id, &owned_card_id).await?
+        }
+        None => club_svc::clear_squad_manager(&state.pool, &club.id).await?,
+    }
+    let manager = club_svc::get_squad_manager(&state.pool, &club.id).await?;
+    Ok(Json(json!({ "manager": manager })))
+}