Upgrade crate and examples to Bevy 0.19

[Copilot]

This PR updates bevy_health_bar3d from Bevy 0.18.1 to 0.19.0, including dependency alignment needed for examples. It also applies the minimal API migrations required for Bevy 0.19 and updates the README compatibility matrix.

• Dependency alignment

  • Bumped bevy to 0.19.0 in both [dependencies] and [dev-dependencies].
  • Updated Bevy-coupled dev deps to compatible releases:
    • bevy-inspector-egui 0.36.0 → 0.37.0
    • bevy_tweening 0.15.0 → 0.16.0
  • Regenerated lockfile for the new resolution set.

• Bevy 0.19 API migrations (library + examples)

  • Updated mutable asset access in src/plugin.rs where material fields are modified.
  • Renamed light field usage in examples:
    • PointLight { shadows_enabled: ... } → PointLight { shadow_maps_enabled: ... }
  • Migrated scene spawning in glTF examples:
    • SceneRoot(handle) → WorldAssetRoot(handle)

• Documentation

  • Added Bevy 0.19 entry to the README compatibility table (>= 3.10.0).

commands.spawn((
    PointLight {
        shadow_maps_enabled: true,
        ..default()
    },
));

commands.spawn(WorldAssetRoot(scene.clone()));

• Fixes Update to Bevy 0.19 #52