Phase 10: card upgrade system (chemistry styles, position change, training)

- GET /chemistry-styles — lists 18 FUT-style chemistry styles with stat boost breakdowns
- POST /collection/:id/chemistry-style — apply a style (Shadow, Hunter, Anchor, etc.)
- POST /collection/:id/position — override a player's position for 500 coins
- POST /collection/:id/training — add +1/+2/+3 OVR training bonus (max +3 total)
- GET /collection now includes chemistry_style, position_override, training_bonus,
  effective_overall and effective_position fields per owned card
- Migration 0007 adds three columns to owned_cards with safe defaults
- 10 new integration tests — all 55 pass, clippy clean

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

src/services/squad.rs

@@ -77,7 +77,7 @@ pub async fn validate_formation(
     let mut gk_count = 0usize;
     for sp in &starters {
         let owned = sqlx::query_as::<_, OwnedCard>(
-            "SELECT id, club_id, card_id, is_loan, loan_matches_remaining, acquired_at FROM owned_cards WHERE id = ?",
+            "SELECT id, club_id, card_id, is_loan, loan_matches_remaining, acquired_at, chemistry_style, position_override, training_bonus FROM owned_cards WHERE id = ?",
         )
         .bind(&sp.owned_card_id)
         .fetch_optional(pool)