Add comprehensive engine tests and fix action field name bugs

Bug fixes in engine.py:
- PlayPokemonAction: card_id -> card_instance_id
- PlayTrainerAction: card_id -> card_instance_id
- UseAbilityAction: pokemon_card_id -> pokemon_id
- SelectActiveAction: card_id -> pokemon_id
- record_ability_use() -> ability_uses_this_turn += 1

Added 26 new tests covering:
- Energy deck setup (Pokemon Pocket style)
- Prize card mode
- Deck size validation (too large)
- PlayPokemonAction (to active, to bench, not found)
- EvolvePokemonAction (success, not in hand, target not found)
- PlayTrainerAction (item, supporter, stadium, replacement)
- UseAbilityAction (success, not found, invalid index)
- SelectActiveAction (forced action, not on bench)
- Deck-out on turn start
- Attack edge cases (no energy, invalid index)
- Retreat without bench
- Attach energy from energy zone

Test count: 711 -> 737 (+26)
Coverage: 89% -> 94% overall, engine.py 55% -> 81%

backend/app/core/engine.py

@@ -450,7 +450,7 @@ class GameEngine:
         action: PlayPokemonAction,
     ) -> ActionResult:
         """Execute playing a Basic Pokemon from hand to bench/active."""
-        card = player.hand.remove(action.card_id)
+        card = player.hand.remove(action.card_instance_id)
         if not card:
             return ActionResult(success=False, message="Card not in hand")
 
@@ -462,7 +462,7 @@ class GameEngine:
                 success=True,
                 message="Played Pokemon to active",
                 state_changes=[
-                    {"type": "play_pokemon", "zone": "active", "card_id": action.card_id}
+                    {"type": "play_pokemon", "zone": "active", "card_id": action.card_instance_id}
                 ],
             )
 
@@ -472,7 +472,9 @@ class GameEngine:
         return ActionResult(
             success=True,
             message="Played Pokemon to bench",
-            state_changes=[{"type": "play_pokemon", "zone": "bench", "card_id": action.card_id}],
+            state_changes=[
+                {"type": "play_pokemon", "zone": "bench", "card_id": action.card_instance_id}
+            ],
         )
 
     def _execute_evolve(
@@ -585,7 +587,7 @@ class GameEngine:
         action: PlayTrainerAction,
     ) -> ActionResult:
         """Execute playing a Trainer card."""
-        card = player.hand.remove(action.card_id)
+        card = player.hand.remove(action.card_instance_id)
         if not card:
             return ActionResult(success=False, message="Card not in hand")
 
@@ -618,7 +620,7 @@ class GameEngine:
                 return ActionResult(
                     success=True,
                     message="Stadium played",
-                    state_changes=[{"type": "play_stadium", "card_id": action.card_id}],
+                    state_changes=[{"type": "play_stadium", "card_id": action.card_instance_id}],
                 )
             elif card_def.trainer_type == TrainerType.ITEM:
                 player.items_played_this_turn += 1
@@ -630,7 +632,7 @@ class GameEngine:
         return ActionResult(
             success=True,
             message="Trainer card played",
-            state_changes=[{"type": "play_trainer", "card_id": action.card_id}],
+            state_changes=[{"type": "play_trainer", "card_id": action.card_instance_id}],
         )
 
     async def _execute_use_ability(
@@ -642,10 +644,10 @@ class GameEngine:
         """Execute using a Pokemon's ability."""
         # Find Pokemon with ability
         pokemon = None
-        if action.pokemon_card_id in player.active:
-            pokemon = player.active.get(action.pokemon_card_id)
-        elif action.pokemon_card_id in player.bench:
-            pokemon = player.bench.get(action.pokemon_card_id)
+        if action.pokemon_id in player.active:
+            pokemon = player.active.get(action.pokemon_id)
+        elif action.pokemon_id in player.bench:
+            pokemon = player.bench.get(action.pokemon_id)
 
         if not pokemon:
             return ActionResult(success=False, message="Pokemon not found")
@@ -659,15 +661,15 @@ class GameEngine:
 
         ability = card_def.abilities[action.ability_index]
 
-        # Mark ability as used
-        pokemon.record_ability_use(action.ability_index)
+        # Mark ability as used (increment counter)
+        pokemon.ability_uses_this_turn += 1
 
         # Execute ability effect (placeholder - would use effect system)
         return ActionResult(
             success=True,
             message=f"Used ability: {ability.name}",
             state_changes=[
-                {"type": "use_ability", "pokemon": action.pokemon_card_id, "ability": ability.name}
+                {"type": "use_ability", "pokemon": action.pokemon_id, "ability": ability.name}
             ],
         )
 
@@ -792,7 +794,7 @@ class GameEngine:
     ) -> ActionResult:
         """Execute selecting a new active Pokemon (forced action)."""
         # Move selected Pokemon from bench to active
-        new_active = player.bench.remove(action.card_id)
+        new_active = player.bench.remove(action.pokemon_id)
         if not new_active:
             return ActionResult(success=False, message="Pokemon not found on bench")
 
@@ -804,7 +806,7 @@ class GameEngine:
         return ActionResult(
             success=True,
             message="New active Pokemon selected",
-            state_changes=[{"type": "select_active", "card_id": action.card_id}],
+            state_changes=[{"type": "select_active", "card_id": action.pokemon_id}],
         )
 
     def _execute_resign(