feat(combat): add activate_power_attack action and consume Up Close and Deadly deed

- New Action kind activate_power_attack: free action that sets
  state.power_attack = True when the combatant has the Power Attack feat;
  logged no-op otherwise. Routed via _execute_movement (free-action branch)
  to keep _execute under the C901 complexity ceiling.
- Consume deed_up_close_and_deadly in resolve_attack: the first attack
  resolved while the flag is set gains +1d6 if it is a ranged attack within
  30 ft; the flag is reset in all cases (benefit lost if out of range or
  not ranged). Extracted into _consume_up_close_and_deadly helper.
- Document activate_power_attack, corrected deed semantics, and the
  power_attack snapshot key in README.
- Add tests/test_engine_fixes.py (5 tests): PA activation, no-feat no-op,
  deed+ranged within 30ft, deed out-of-range, deed melee.

src/pf1e_simulator/combat.py

@@ -489,6 +489,7 @@ class Action:
         "full_attack", "charge", "withdraw", "5foot_step", "cast_spell",
         "maneuver", "channel_energy", "hex", "deed", "spell_combat",
         "inspire_courage", "retrieve_weapon", "repair_weapon",
+        "activate_power_attack",
     ]
     target_id: str | None = None
     spell_name: str | None = None
@@ -1373,12 +1374,40 @@ class CombatEngine:
                 damage *= weapon.crit_mult
             damage = self._apply_dr(damage, weapon, target)
         target.hp -= damage
+        damage = self._consume_up_close_and_deadly(
+            attacker, target, weapon, dist_ft, damage, hit=hit
+        )
         return AttackResult(
             hit=hit, crit=crit, damage=damage, roll=roll, total=total, ac=ac,
             penalty=penalty, flank_bonus=flank, high_ground_bonus=high_ground,
             base_bonus=base_bonus,
         )
 
+    def _consume_up_close_and_deadly(
+        self,
+        attacker: CombatantState,
+        target: CombatantState,
+        weapon: AttackSpec,
+        dist_ft: int,
+        damage: int,
+        *,
+        hit: bool,
+    ) -> int:
+        """Consume the Up Close and Deadly deed on the first attack resolved.
+
+        The deed applies +1d6 to a ranged attack within 30 ft; the flag is
+        reset after the first attack in all cases (the benefit is lost if the
+        attack is out of range or not ranged).
+        """
+        if not attacker.deed_up_close_and_deadly:
+            return damage
+        if hit and self._is_ranged_attack(weapon) and dist_ft <= _UP_CLOSE_RANGE_FT:
+            bonus = self._rng.roll_die(6)
+            damage += bonus
+            target.hp -= bonus
+        attacker.deed_up_close_and_deadly = False
+        return damage
+
     def _apply_dr(self, damage: int, weapon: AttackSpec, target: CombatantState) -> int:
         dr: DamageReduction | None = target.combatant.dr
         if dr is None:
@@ -1990,6 +2019,8 @@ class CombatEngine:
             self._move(state, target)
         elif kind == "wait":
             self._log(f"round {self._current_round} {state.combatant.id}: wait")
+        elif kind == "activate_power_attack":
+            self._execute_activate_power_attack(state)
 
     def _execute_immediate(
         self, state: CombatantState, target: CombatantState | None, action: Action
@@ -2011,6 +2042,20 @@ class CombatEngine:
         elif target is not None:
             self._execute_attack(state, target, "attack")
 
+    def _execute_activate_power_attack(self, state: CombatantState) -> None:
+        """Activate Power Attack as a free action (requires the feat)."""
+        if not self._has_feat(state, "Power Attack"):
+            self._log(
+                f"round {self._current_round} {state.combatant.id}: "
+                f"activate_power_attack: no Power Attack feat"
+            )
+            return
+        state.power_attack = True
+        self._log(
+            f"round {self._current_round} {state.combatant.id}: "
+            f"Power Attack activated"
+        )
+
     def _check_reactions(self, event: ReactionEvent) -> None:
         """Offer an event to the reaction policy; execute the first immediate.