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_engine/src/cursor_plugin.rs

@@ -331,7 +331,11 @@ fn update_drop_target_overlays(
 /// for everything else it is card-sized. Replicated here rather than
 /// imported because `pile_drop_rect` is private to `input_plugin` and
 /// this overlay is the only other consumer.
-fn drop_overlay_rect(pile: &KlondikePile, layout: &Layout, game: &GameState) -> Option<(Vec2, Vec2)> {
+fn drop_overlay_rect(
+    pile: &KlondikePile,
+    layout: &Layout,
+    game: &GameState,
+) -> Option<(Vec2, Vec2)> {
     let centre = layout.pile_positions.get(pile).copied()?;
     if matches!(pile, KlondikePile::Tableau(_)) {
         let card_count = game.pile(*pile).len();
@@ -619,7 +623,7 @@ mod tests {
         drag.committed = true;
     }
 
-        #[test]
+    #[test]
     fn drop_target_overlay_does_not_spawn_for_invalid_destination() {
         // 5 of Spades (black) onto Tableau(2)'s 6 of Clubs (also black)
         // — same colour family, illegal. Tableau(2) must NOT be
@@ -658,5 +662,4 @@ mod tests {
             "Tableau(2) must not be highlighted for an illegal drop, got {overlays:?}"
         );
     }
-
-    }
+}