fix(engine,wasm,web): detect no-legal-moves correctly and surface banner

Engine: replace broken has_legal_moves loop (which checked buried
mid-column cards without sequence validation) with a delegation to
possible_instructions(), mirroring the hint system's logic exactly.

WASM: add has_moves: bool to GameSnapshot, computed in snap() using the
same stock/waste/possible_instructions check so the web client gets the
flag in every state update at no extra round-trip cost.

Web: show a non-blocking no-moves banner (slide-up toast) with Undo and
New Game actions when has_moves is false and the game is not won. Banner
hides automatically once a move restores legal play (e.g. after undo).

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

solitaire_wasm/src/lib.rs

@@ -241,6 +241,8 @@ pub struct GameSnapshot {
     pub move_count: u32,
     pub is_won: bool,
     pub is_auto_completable: bool,
+    /// `false` when stock, waste, and all pile-to-pile moves are exhausted.
+    pub has_moves: bool,
     pub undo_count: u32,
     /// Number of snapshots currently on the undo stack; 0 means undo is unavailable.
     pub undo_stack_len: usize,
@@ -279,11 +281,17 @@ impl SolitaireGame {
                 .map(|p| p.cards.iter().map(CardSnapshot::from).collect())
                 .unwrap_or_default()
         };
+        let has_moves = {
+            let stock_empty = self.game.piles.get(&PileType::Stock).is_none_or(|p| p.cards.is_empty());
+            let waste_empty = self.game.piles.get(&PileType::Waste).is_none_or(|p| p.cards.is_empty());
+            !stock_empty || !waste_empty || !self.game.possible_instructions().is_empty()
+        };
         GameSnapshot {
             score: self.game.score,
             move_count: self.game.move_count,
             is_won: self.game.is_won,
             is_auto_completable: self.game.is_auto_completable,
+            has_moves,
             undo_count: self.game.undo_count,
             undo_stack_len: self.game.undo_stack_len(),
             stock: cards(PileType::Stock),