Offer a Continue link for ongoing games in the lobby

A player who accidentally closes the game page can now get back to it
from the lobby.

Backend:
- GameStore.list_ongoing() returns live unfinished sessions (newest
  first), skipping expired keys and finished matches;
- GET /api/me/games lists the games the caller is seated in, with the
  game name/description, players, open seats and your seat (no join
  code);
- store, platform route and app integration tests.

Frontend:
- MyGame/MyGamesPage model plus api::my_games();
- the lobby shows a "Your games" card with phase, seats, players and a
  Continue button linking to /game/<id>; hidden when empty or logged
  out.

web/src/api.rs

@@ -128,6 +128,20 @@ pub async fn probe_game(game_id: &str) -> GameEntry {
     }
 }
 
+/// Fetch the live games the caller is seated in, for the lobby's
+/// "Continue" list.
+pub async fn my_games() -> Result<Vec<MyGame>, String> {
+    let resp = Request::get("/api/me/games")
+        .send()
+        .await
+        .map_err(|e| e.to_string())?;
+    if !resp.ok() {
+        return Err(server_error(resp.status()));
+    }
+    let page: MyGamesPage = resp.json().await.map_err(|e| e.to_string())?;
+    Ok(page.results)
+}
+
 pub async fn my_matches(cursor: Option<&str>) -> Result<MatchesPage, String> {
     let url = match cursor {
         Some(c) => format!("/api/me/matches?limit=10&cursor={c}"),