fix(rules): natural weapons get no BAB iteratives, secondary attacks at -5

PF1e (CRB "Natural Attacks"):
- Natural weapons (natural=true) get exactly one swing per full attack,
  regardless of BAB (no BAB iteratives for natural attacks).
- Secondary natural attacks (secondary=true) attack at BAB -5; the
  Multiattack feat reduces this to -2.
- Manifested in combat.py (_full_attack_weapon, _resolve_swing),
  models.py (AttackSpec.natural/secondary), 6 data JSONs, 4 new tests,
  and README documentation.

1461 passed, ruff clean, basedpyright 0 errors.

src/pf1e_simulator/models.py

@@ -242,14 +242,18 @@ class AttackSpec(_FrozenModel):
     increment and against full AC beyond it. `two_handed` marks a weapon swung
     in two hands (two-handed weapon, one-handed weapon used two hands, or a
     primary natural with 1.5x Strength) — PF1e Power Attack rolls +50% damage
-    with such a weapon (CRB "Power Attack"). `reach_weapon` marks a weapon
+    with such a weapon (CRB "Power Attack").     `reach_weapon` marks a weapon
     with the reach weapon quality (CRB "Big and Little Creatures in Combat"):
     it doubles the wielder's NATURAL reach but cannot strike at the wielder's
     natural reach or less — the usable zone is a RING (dead zone = natural
     reach). Without the flag a melee attack follows the creature's natural
     reach, which is a DISK: a Large creature's natural attack (its JSON
     `reach_ft` IS its natural reach, 10 ft) still strikes and threatens
-    adjacent squares.
+    adjacent squares. `natural` marks a natural weapon (bite, claw, etc.):
+    PF1e (CRB "Natural Attacks") grants no BAB iteratives for natural
+    weapons. `secondary` marks a secondary natural attack (tail, wing, etc.):
+    the engine applies -5 to the attack bonus (reduced to -2 with the
+    Multiattack feat).
     """
 
     id: str
@@ -266,6 +270,8 @@ class AttackSpec(_FrozenModel):
     count: int = Field(default=1, ge=1)
     firearm: bool = False
     two_handed: bool = False
+    natural: bool = False
+    secondary: bool = False
 
 
 class DamageReduction(_FrozenModel):