Phase 15: add GET /packs/store endpoint

Returns all pack definitions with id, name, description, cost_coins, and
total_cards so the dashboard can render a purchasable pack store without
needing to know the definitions at compile time.

Two new tests: store listing shape and buy-then-open round-trip.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/routes/packs.rs

@@ -35,6 +35,25 @@ pub async fn post_buy_pack(
     ))
 }
 
+/// List all purchasable pack definitions with their coin costs.
+pub async fn get_pack_store(State(state): State<AppState>) -> AppResult<Json<Value>> {
+    let store: Vec<Value> = state
+        .pack_defs
+        .iter()
+        .map(|d| {
+            let total_cards: u8 = d.slots.iter().map(|s| s.count).sum();
+            json!({
+                "id": d.id,
+                "name": d.name,
+                "description": d.description,
+                "cost_coins": d.cost_coins,
+                "total_cards": total_cards,
+            })
+        })
+        .collect();
+    Ok(Json(json!({ "packs": store })))
+}
+
 pub async fn get_packs(State(state): State<AppState>) -> AppResult<Json<Value>> {
     let profile = profile_svc::get_active_profile(&state.pool).await?;
     let club = club_svc::get_club_by_profile(&state.pool, &profile.id).await?;