fix(engine): resolve input coordination bugs in selection/pause/keyboard

- SelectionPlugin: add clear_selection_on_state_change system so undo/move/reject
  never leave a stale selection pointing at the wrong card
- SelectionPlugin: expose SelectionKeySet system set for cross-plugin ordering
- PausePlugin: skip Escape→pause when a card is keyboard-selected; toggle_pause
  now runs before SelectionKeySet so it reads SelectionState before it is cleared
- InputPlugin: guard Space→DrawRequestEvent when SelectionState has an active pile
  so Space executes a card move instead of also drawing from stock
- window: enforce 800×600 minimum via WindowResizeConstraints
- game_state: add precondition doc to next_auto_complete_move (waste exclusion)
- card_plugin: 12 unit tests for constants, face_colour, label_visibility, label_for
- pause_plugin: add paused_resource_default and draw_mode_label exhaustiveness tests

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

solitaire_engine/src/selection_plugin.rs

@@ -22,7 +22,7 @@ use solitaire_core::card::Suit;
 use solitaire_core::pile::PileType;
 
 use crate::card_plugin::CardEntity;
-use crate::events::{InfoToastEvent, MoveRequestEvent};
+use crate::events::{InfoToastEvent, MoveRequestEvent, StateChangedEvent};
 use crate::game_plugin::GameMutation;
 use crate::input_plugin::{best_destination, best_tableau_destination_for_stack};
 use crate::layout::LayoutResource;
@@ -42,6 +42,13 @@ pub struct SelectionState {
     pub selected_pile: Option<PileType>,
 }
 
+/// System set label for the key-handling system.
+///
+/// `PausePlugin` registers `toggle_pause` before this set so it can read
+/// [`SelectionState`] before `handle_selection_keys` clears it on Escape.
+#[derive(SystemSet, Debug, Clone, PartialEq, Eq, Hash)]
+pub struct SelectionKeySet;
+
 /// Marker component placed on the outline sprite used as the keyboard-selection
 /// highlight.
 ///
@@ -59,7 +66,10 @@ impl Plugin for SelectionPlugin {
             .add_systems(
                 Update,
                 (
-                    handle_selection_keys.before(GameMutation),
+                    handle_selection_keys
+                        .in_set(SelectionKeySet)
+                        .before(GameMutation),
+                    clear_selection_on_state_change.after(GameMutation),
                     update_selection_highlight.after(GameMutation),
                 ),
             );
@@ -329,6 +339,20 @@ fn try_foundation_dest(
     None
 }
 
+/// Clears the selection whenever the game state changes.
+///
+/// Without this, an undo or a rejected move could leave `selected_pile`
+/// pointing at a pile whose top card changed, causing the highlight to
+/// trail a different card than the player expects.
+fn clear_selection_on_state_change(
+    mut state_events: MessageReader<StateChangedEvent>,
+    mut selection: ResMut<SelectionState>,
+) {
+    if state_events.read().next().is_some() {
+        selection.selected_pile = None;
+    }
+}
+
 /// Maintains the `SelectionHighlight` outline sprite.
 ///
 /// When a pile is selected, a cyan sprite is placed at the selected card's