feat: Phase 2 — game feel complete

Chemistry & squads:
- Chemistry calculation on GET /squad (club/league/nation links, max 100)
- Formation validation on POST /squad (exactly 11 starters, exactly 1 GK)

Objectives:
- Weekly objectives JSON (4 objectives: warrior, goals, dedicated, SBC)
- Daily objectives auto-reset at midnight UTC (background task)

SBC validation expanded:
- max_overall per-player enforcement
- required_clubs validation
- min_players_from_same_nation validation
- min_players_from_same_club validation

Market:
- GET /market?min_overall=X&position=Y filtering
- Expiry cleanup runs before every NPC refresh
- NPC market auto-refresh every 24h (background task, runs at startup)

Matches:
- GET /matches/opponent?difficulty=beginner|professional|world_class|legendary
  generates a random AI opponent squad from the card pool

Statistics:
- win_streak and best_win_streak tracking (migration 0002)
- GET /statistics/history?limit=N — last N matches with summary stats

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

src/models/statistics.rs

@@ -12,6 +12,8 @@ pub struct Statistics {
     pub packs_opened: i64,
     pub sbcs_completed: i64,
     pub total_coins_earned: i64,
+    pub win_streak: i64,
+    pub best_win_streak: i64,
     pub updated_at: String,
 }
 
@@ -28,6 +30,8 @@ impl Statistics {
             packs_opened: 0,
             sbcs_completed: 0,
             total_coins_earned: 0,
+            win_streak: 0,
+            best_win_streak: 0,
             updated_at: chrono::Utc::now().to_rfc3339(),
         }
     }