chore: cargo fmt across workspace; add analytics domain to CSP

- Apply cargo fmt to solitaire_engine, solitaire_server formatting.
- solitaire_server/src/lib.rs: add https://analytics.aleshym.co to
  script-src, img-src, and connect-src so the analytics beacon loads
  without a CSP violation.
- docs and README updates.

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

solitaire_server/src/sync.rs

@@ -196,14 +196,11 @@ async fn update_leaderboard_if_opted_in(
     user_id: &str,
     payload: &SyncPayload,
 ) -> Result<(), AppError> {
-    let opted_in = sqlx::query!(
-        "SELECT leaderboard_opt_in FROM users WHERE id = ?",
-        user_id
-    )
-    .fetch_optional(pool)
-    .await?
-    .map(|r| r.leaderboard_opt_in)
-    .unwrap_or(0);
+    let opted_in = sqlx::query!("SELECT leaderboard_opt_in FROM users WHERE id = ?", user_id)
+        .fetch_optional(pool)
+        .await?
+        .map(|r| r.leaderboard_opt_in)
+        .unwrap_or(0);
 
     if opted_in != 1 {
         return Ok(());