Rename galaxy_creation to galaxy; add character creation skeleton

- Rename GalaxyCreationPlugin -> GalaxyPlugin, AppState::GalaxyCreation
  -> AppState::Galaxy, module path galaxy_creation -> galaxy (folder
  rename preserves git history via git mv).
- Rename GalaxyCreationSpawned -> GalaxySpawned, despawn_galaxy_creation
  -> despawn_galaxy.
- Update AGENTS.md module layout, plugin pattern example, and naming
  table for the new names.
- Add apps/game/src/gameplay/character_creation/ skeleton: placeholder
  UI with Confirm (-> InGame) and Back (-> Galaxy) buttons plus Escape
  shortcut. Wired into main.rs via CharacterCreationPlugin.

apps/game/src/gameplay/character_creation/mod.rs

@@ -0,0 +1,194 @@
+//! Character creation scene.
+//!
+//! Barebones skeleton: spawns a placeholder UI on enter, despawns on exit,
+//! and wires a `Confirm` button that transitions to [`AppState::InGame`] and
+//! a `Back` button (or Escape) that returns to [`AppState::Galaxy`].
+//!
+//! Intended to grow into the real character creator — name, portrait, stats,
+//! starting ship, background / origin, etc. Each major aspect should split
+//! into its own submodule (e.g. `ui.rs`, `params.rs`, `presets.rs`) once it
+//! outgrows this file (see the module-layout guidelines in `apps/game/AGENTS.md`).
+
+use bevy::prelude::*;
+
+use crate::state::AppState;
+
+pub struct CharacterCreationPlugin;
+
+impl Plugin for CharacterCreationPlugin {
+    fn build(&self, app: &mut App) {
+        app.add_systems(OnEnter(AppState::CharacterCreation), setup_character_creation)
+            .add_systems(
+                OnExit(AppState::CharacterCreation),
+                despawn_character_creation,
+            )
+            .add_systems(
+                Update,
+                (
+                    escape_to_galaxy,
+                    confirm_button_handler,
+                    back_button_handler,
+                )
+                    .run_if(in_state(AppState::CharacterCreation)),
+            );
+    }
+}
+
+// ── Markers ─────────────────────────────────────────────────────────────────
+
+/// Tag for everything spawned during character creation so it can be cleanly
+/// despawned on state exit.
+#[derive(Component)]
+pub struct CharacterCreationSpawned;
+
+#[derive(Component)]
+pub enum CharacterCreationButton {
+    /// Finalize the character and begin the game.
+    Confirm,
+    /// Discard and return to the galaxy selection screen.
+    Back,
+}
+
+// ── Setup ───────────────────────────────────────────────────────────────────
+
+fn setup_character_creation(mut commands: Commands) {
+    let button_style = Node {
+        width: Val::Px(220.0),
+        height: Val::Px(56.0),
+        justify_content: JustifyContent::Center,
+        align_items: AlignItems::Center,
+        ..default()
+    };
+    let button_font = TextFont {
+        font_size: 24.0,
+        ..default()
+    };
+
+    commands
+        .spawn((
+            Node {
+                width: Val::Percent(100.0),
+                height: Val::Percent(100.0),
+                display: Display::Flex,
+                flex_direction: FlexDirection::Column,
+                justify_content: JustifyContent::Center,
+                align_items: AlignItems::Center,
+                row_gap: Val::Px(24.0),
+                ..default()
+            },
+            BackgroundColor(Color::srgb(0.02, 0.02, 0.06)),
+            CharacterCreationSpawned,
+        ))
+        .with_children(|parent| {
+            parent.spawn((
+                Text::new("Character Creation"),
+                TextFont {
+                    font_size: 56.0,
+                    ..default()
+                },
+                TextColor(Color::srgb(0.7, 0.85, 1.0)),
+                Node {
+                    margin: UiRect::bottom(Val::Px(16.0)),
+                    ..default()
+                },
+            ));
+
+            parent.spawn((
+                Text::new("TODO: name, portrait, stats, background, starting ship"),
+                TextFont {
+                    font_size: 18.0,
+                    ..default()
+                },
+                TextColor(Color::srgb(0.4, 0.5, 0.6)),
+                Node {
+                    margin: UiRect::bottom(Val::Px(48.0)),
+                    ..default()
+                },
+            ));
+
+            spawn_button(
+                &mut parent.spawn_empty(),
+                "Confirm",
+                CharacterCreationButton::Confirm,
+                &button_style,
+                &button_font,
+            );
+            spawn_button(
+                &mut parent.spawn_empty(),
+                "Back",
+                CharacterCreationButton::Back,
+                &button_style,
+                &button_font,
+            );
+        });
+}
+
+fn spawn_button(
+    cmd: &mut EntityCommands,
+    label: &str,
+    marker: CharacterCreationButton,
+    style: &Node,
+    text_font: &TextFont,
+) {
+    cmd.insert((
+        Button,
+        style.clone(),
+        BackgroundColor(Color::srgb(0.08, 0.1, 0.18)),
+        BorderColor(Color::srgb(0.3, 0.45, 0.7)),
+        BorderRadius::all(Val::Px(8.0)),
+        marker,
+    ))
+    .with_children(|btn| {
+        btn.spawn((
+            Text::new(label),
+            text_font.clone(),
+            TextColor(Color::srgb(0.75, 0.85, 1.0)),
+        ));
+    });
+}
+
+// ── Lifecycle ───────────────────────────────────────────────────────────────
+
+fn despawn_character_creation(
+    mut commands: Commands,
+    query: Query<Entity, With<CharacterCreationSpawned>>,
+) {
+    for entity in &query {
+        // Bevy 0.16: despawn() is recursive by default.
+        commands.entity(entity).despawn();
+    }
+}
+
+// ── Input ───────────────────────────────────────────────────────────────────
+
+fn escape_to_galaxy(
+    keys: Res<ButtonInput<KeyCode>>,
+    mut next_state: ResMut<NextState<AppState>>,
+) {
+    if keys.just_pressed(KeyCode::Escape) {
+        next_state.set(AppState::Galaxy);
+    }
+}
+
+fn confirm_button_handler(
+    mut next_state: ResMut<NextState<AppState>>,
+    query: Query<(&Interaction, &CharacterCreationButton), Changed<Interaction>>,
+) {
+    for (interaction, button) in &query {
+        if *interaction == Interaction::Pressed && matches!(button, CharacterCreationButton::Confirm) {
+            // TODO: persist the configured character before entering the game.
+            next_state.set(AppState::InGame);
+        }
+    }
+}
+
+fn back_button_handler(
+    mut next_state: ResMut<NextState<AppState>>,
+    query: Query<(&Interaction, &CharacterCreationButton), Changed<Interaction>>,
+) {
+    for (interaction, button) in &query {
+        if *interaction == Interaction::Pressed && matches!(button, CharacterCreationButton::Back) {
+            next_state.set(AppState::Galaxy);
+        }
+    }
+}