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/db.rs

@@ -10,6 +10,10 @@ pub async fn init_pool(database_url: &str) -> Result<Pool> {
         .max_connections(5)
         .connect(database_url)
         .await?;
+    sqlx::query("PRAGMA journal_mode=WAL")
+        .execute(&pool)
+        .await?;
+    sqlx::query("PRAGMA foreign_keys=ON").execute(&pool).await?;
     Ok(pool)
 }