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/models/chemistry_style.rs

@@ -0,0 +1,26 @@
+use serde::{Deserialize, Serialize};
+
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct StatBoosts {
+    pub pace: i32,
+    pub shooting: i32,
+    pub passing: i32,
+    pub dribbling: i32,
+    pub defending: i32,
+    pub physical: i32,
+}
+
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct ChemistryStyle {
+    pub id: String,
+    pub name: String,
+    pub description: String,
+    pub boosts: StatBoosts,
+}
+
+pub fn load_chemistry_styles(data_dir: &str) -> anyhow::Result<Vec<ChemistryStyle>> {
+    let path = format!("{data_dir}/chemistry_styles.json");
+    let raw = std::fs::read_to_string(&path)
+        .map_err(|e| anyhow::anyhow!("failed to read {path}: {e}"))?;
+    Ok(serde_json::from_str(&raw)?)
+}