fix(boosters): count hammer/line-bomb clears toward objectives and win

Owner playtesting found that hammering a gem (or line-bombing a gem line)
removed it visually but did not satisfy the clear-gems objective and never
completed the stage — it felt broken. Per owner decision, booster clears
now count: a hammered gem emits gems:1, a line-bomb emits lines:1 + the
line's gem count, both folded through the objectives. After any booster the
engine resolves the phase (completed objective -> won, else re-check stuck),
which was the direct cause of the stage not finishing. Score and the move
counter remain untouched. Reverses the earlier no-objective-credit rule.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

lib/game/engine/game_engine.dart

@@ -217,19 +217,22 @@ class GameEngine {
     _phase = GamePhase.lost;
   }
 
-  /// Booster: empties one filled cell. No move/score/combo/objective effect.
-  /// Allowed only mid-attempt (playing or stuck). Returns false on an empty
-  /// cell or finished attempt so the caller keeps the booster.
+  /// Booster: empties one filled cell. No move/score/combo effect, but a
+  /// hammered gem DOES count toward a clear-gems objective (and can win the
+  /// stage). Allowed only mid-attempt. Returns false on an empty cell or a
+  /// finished attempt so the caller keeps the booster.
   bool useHammer(int x, int y) {
     if (_phase == GamePhase.won || _phase == GamePhase.lost) return false;
     if (!_grid.isOccupied(x, y)) return false;
+    final wasGem = _grid.cellAt(x, y).type == CellType.gem;
     _grid = _grid.withCell(x, y, const Cell(CellType.empty));
-    _checkStuck();
+    _resolveAfterBooster(
+        wasGem ? const LinesCleared(lines: 0, gems: 1) : null);
     return true;
   }
 
-  /// Booster: re-deals the tray. No move/score effect. Re-checks stuck so a
-  /// dead board with a hopeless tray can become playable again.
+  /// Booster: re-deals the tray. No move/score/objective effect. Re-checks
+  /// stuck so a dead board with a hopeless tray can become playable again.
   bool useShuffle() {
     if (_phase == GamePhase.won || _phase == GamePhase.lost) return false;
     _tray = _generator.nextTray(_grid);
@@ -237,17 +240,35 @@ class GameEngine {
     return true;
   }
 
-  /// Booster: empties one row or one column (exactly one of [row]/[col]).
-  /// No move/score/objective effect. Re-checks stuck.
+  /// Booster: empties one row or one column (exactly one of [row]/[col]). No
+  /// move/score effect, but it counts as clearing one line plus any gems on
+  /// that line, toward the stage objectives (and can win the stage).
   bool useLineBomb({int? row, int? col}) {
     if (_phase == GamePhase.won || _phase == GamePhase.lost) return false;
     if ((row == null) == (col == null)) return false; // need exactly one
+    var gems = 0;
     for (var i = 0; i < GridState.size; i++) {
       final x = col ?? i;
       final y = row ?? i;
+      if (_grid.cellAt(x, y).type == CellType.gem) gems++;
       _grid = _grid.withCell(x, y, const Cell(CellType.empty));
     }
-    _checkStuck();
+    _resolveAfterBooster(LinesCleared(lines: 1, gems: gems));
     return true;
   }
+
+  /// After a booster mutates the grid, feed any [cleared] event through the
+  /// objectives so booster-cleared gems/lines count, then resolve the phase:
+  /// a completed objective wins the stage, otherwise re-check stuck. Score and
+  /// the move counter stay untouched — boosters are help, not a placement.
+  void _resolveAfterBooster(LinesCleared? cleared) {
+    if (cleared != null) {
+      _objectives = [for (final obj in _objectives) obj.onEvent(cleared)];
+    }
+    if (!_stage.endless && _objectives.every((o) => o.isComplete)) {
+      _phase = GamePhase.won;
+    } else {
+      _checkStuck();
+    }
+  }
 }