Phase 7 (Core): chemistry v2, expanded card pool & search filters

- Chemistry v2: FUT-style link scoring with per-player breakdown
  (club +3/link cap 6, league +1/link cap 4, nation +1/link cap 3;
   player cap 10, team cap 100); chemistry response now includes
   per-player breakdown with club/league/nation link counts and pts
- Card pool: 34 new cards across Premier League, La Liga, Bundesliga
  with overlapping clubs/nations for meaningful chemistry testing
- Card search: extended GET /cards with nation, league, club,
  min_overall, max_overall, limit query params; results sorted by
  overall descending
- Match opponent: added "ultimate" difficulty band (85+ OVR);
  random formation selection from 6 tactical formations; falls back
  to lower OVR pool when not enough cards at the requested band
- Tests: 9 new integration tests (28 total, all passing)

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

src/routes/cards.rs

@@ -16,6 +16,12 @@ use crate::{
 pub struct CardQuery {
     pub rarity: Option<String>,
     pub position: Option<String>,
+    pub nation: Option<String>,
+    pub league: Option<String>,
+    pub club: Option<String>,
+    pub min_overall: Option<u8>,
+    pub max_overall: Option<u8>,
+    pub limit: Option<usize>,
 }
 
 pub async fn get_card(
@@ -33,25 +39,49 @@ pub async fn get_cards(
     State(state): State<AppState>,
     Query(query): Query<CardQuery>,
 ) -> AppResult<Json<Value>> {
-    let cards = state
+    let mut cards: Vec<_> = state
         .card_db
         .all()
         .into_iter()
         .filter(|c| {
-            query
+            let rarity_ok = query
                 .rarity
                 .as_ref()
                 .map(|r| format!("{:?}", c.rarity).to_lowercase() == r.to_lowercase())
-                .unwrap_or(true)
-                && query
-                    .position
-                    .as_ref()
-                    .map(|p| c.position.to_lowercase() == p.to_lowercase())
-                    .unwrap_or(true)
+                .unwrap_or(true);
+            let pos_ok = query
+                .position
+                .as_ref()
+                .map(|p| c.position.eq_ignore_ascii_case(p))
+                .unwrap_or(true);
+            let nation_ok = query
+                .nation
+                .as_ref()
+                .map(|n| c.nation.eq_ignore_ascii_case(n))
+                .unwrap_or(true);
+            let league_ok = query
+                .league
+                .as_ref()
+                .map(|l| c.league.eq_ignore_ascii_case(l))
+                .unwrap_or(true);
+            let club_ok = query
+                .club
+                .as_ref()
+                .map(|cl| c.club.eq_ignore_ascii_case(cl))
+                .unwrap_or(true);
+            let min_ok = query.min_overall.map(|m| c.overall >= m).unwrap_or(true);
+            let max_ok = query.max_overall.map(|m| c.overall <= m).unwrap_or(true);
+            rarity_ok && pos_ok && nation_ok && league_ok && club_ok && min_ok && max_ok
         })
-        .collect::<Vec<_>>();
+        .collect();
 
-    Ok(Json(json!({ "cards": cards, "total": cards.len() })))
+    cards.sort_by_key(|c| std::cmp::Reverse(c.overall));
+    let total = cards.len();
+    if let Some(limit) = query.limit {
+        cards.truncate(limit);
+    }
+
+    Ok(Json(json!({ "cards": cards, "total": total, "returned": cards.len() })))
 }
 
 pub async fn get_collection(State(state): State<AppState>) -> AppResult<Json<Value>> {