feat: Phase 1 — core game loop complete

New endpoints:
- GET  /cards/:card_id       single card lookup
- POST /packs/buy            purchase pack with coins
- POST /objectives/claim     claim completed objective reward
- GET  /matches              match history (limit/mode query params)
- GET  /sbc/:sbc_id          single SBC lookup

Card pool expanded:
- Bronze: 11 → 30 cards (19 nations)
- Silver: 0 → 20 cards (20 nations)
- Rare Gold: 0 → 10 cards (10 nations)

SBC pool expanded:
- Added 5 new SBCs (tri_nations, silver_to_gold, league_loyalty,
  african_stars, gold_standard)

Infrastructure:
- SQLite WAL mode enabled on pool init
- Foreign key enforcement enabled

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

src/services/pack.rs

@@ -133,6 +133,23 @@ pub async fn open_pack(
     })
 }
 
+pub async fn buy_pack(
+    pool: &Pool,
+    pack_defs: &[PackDefinition],
+    club_id: &str,
+    definition_id: &str,
+) -> AppResult<Pack> {
+    let def = pack_defs
+        .iter()
+        .find(|d| d.id == definition_id)
+        .ok_or_else(|| {
+            AppError::NotFound(format!("pack definition '{definition_id}' not found"))
+        })?;
+
+    crate::services::club::spend_coins(pool, club_id, def.cost_coins).await?;
+    grant_pack(pool, club_id, definition_id).await
+}
+
 pub async fn get_unopened_packs(pool: &Pool, club_id: &str) -> AppResult<Vec<Pack>> {
     let packs = sqlx::query_as::<_, Pack>(
         "SELECT id, club_id, definition_id, opened, created_at FROM packs WHERE club_id = ? AND opened = 0"