chore(deps): migrate to Bevy 0.16, axum 0.8, and other package updates

- Bump bevy 0.15 → 0.16; fixes all breaking API changes:
  ChildBuilder → ChildSpawnerCommands, Parent → ChildOf,
  despawn_descendants → despawn_related::<Children>(),
  despawn_recursive → despawn (now recursive by default),
  EventWriter::send → write, Query::{get_single,get_single_mut}
  → {single,single_mut}, ChildOf::get → parent()
- Bump axum 0.7 → 0.8; remove axum::async_trait from FromRequestParts
- Bump tower_governor 0.4 → 0.8; fix GovernorLayer::new() API
- Bump jsonwebtoken 9 → 10 with rust_crypto feature only
- Bump thiserror 1 → 2, dirs 5 → 6, bcrypt 0.15 → 0.19,
  reqwest 0.12 → 0.13 (rustls feature rename)
- Regenerate .sqlx offline cache for sqlx compile-time query checks

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

solitaire_engine/src/cursor_plugin.rs

@@ -52,7 +52,7 @@ fn update_cursor_icon(
     game: Option<Res<GameStateResource>>,
     mut commands: Commands,
 ) {
-    let Ok((win_entity, window)) = windows.get_single() else { return };
+    let Ok((win_entity, window)) = windows.single() else { return };
 
     if !drag.is_idle() {
         commands
@@ -63,7 +63,7 @@ fn update_cursor_icon(
 
     let hovering = (|| {
         let cursor = window.cursor_position()?;
-        let (camera, cam_xf) = cameras.get_single().ok()?;
+        let (camera, cam_xf) = cameras.single().ok()?;
         let world = camera.viewport_to_world_2d(cam_xf, cursor).ok()?;
         let layout = layout.as_ref()?.0.clone();
         let game = game.as_ref()?;