Scope the leaderboard to a selectable game

Elo ratings are stored per game type, so the leaderboard now always
requests /api/leaderboard?game_type=<id> and shows only that game's
players, Elo, wins, matches and points instead of mixing all games'
aggregates with the default game's rating.

- api::leaderboard takes the game type;
- a "Game" dropdown next to the heading lists every registered game and
  reloads the board on change (stale in-flight responses are dropped);
- move fallback_game_types() from the lobby to model.rs so both the
  lobby and leaderboard selectors work when /api/game-types fails.

web/src/pages/lobby.rs

@@ -15,39 +15,10 @@ use crate::api;
 use crate::components::card::card_back;
 use crate::components::toast::toast;
 use crate::model::{
-    AuthProvider, GameTypeInfo, JoinPreview, OptionField, OptionKind, PlayerRating, User,
+    fallback_game_types, AuthProvider, GameTypeInfo, JoinPreview, OptionField, OptionKind,
+    PlayerRating, User,
 };
 
-/// Used when the game-types fetch fails: match creation must still work.
-fn fallback_game_types() -> Vec<GameTypeInfo> {
-    vec![
-        GameTypeInfo {
-            id: "scopone_scientifico".to_string(),
-            name: "Scopone scientifico".to_string(),
-            description: String::new(),
-            min_players: 4,
-            max_players: 4,
-            options_schema: serde_json::Value::Null,
-        },
-        GameTypeInfo {
-            id: "briscola".to_string(),
-            name: "Briscola".to_string(),
-            description: String::new(),
-            min_players: 2,
-            max_players: 2,
-            options_schema: serde_json::Value::Null,
-        },
-        GameTypeInfo {
-            id: "briscola_a_quattro".to_string(),
-            name: "Briscola a quattro".to_string(),
-            description: String::new(),
-            min_players: 4,
-            max_players: 4,
-            options_schema: serde_json::Value::Null,
-        },
-    ]
-}
-
 /// Human-readable label for a provider name ("google" -> "Google").
 fn provider_label(name: &str) -> String {
     let mut chars = name.chars();