fix(rules): distinguish natural reach from reach weapons

PF1e CRB 'Big and Little Creatures in Combat': a creature's natural
reach is a disk (a Large creature still threatens and strikes adjacent
squares), while a reach weapon doubles the wielder's natural reach but
'can't strike at their natural reach or less' (a ring whose dead zone is
the natural reach). The engine keyed the ring off reach_ft > 5, so
reach-10 natural attacks (giant belostomatid bite/claw, mounted
hooves) wrongly got a 5-ft dead zone.

AttackSpec gains reach_weapon (parsed from the combatant JSON); the
disk-vs-ring rule is centralized in _melee_reach_zone_cells and applied
consistently to weapon selection, melee usability, threatened squares
and charge end placement. Esha's Lance is the only reach weapon in the
shipped data; Large natural attackers keep the default (disk).

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

src/pf1e_simulator/models.py

@@ -242,7 +242,14 @@ 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").
+    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.
     """
 
     id: str
@@ -254,6 +261,7 @@ class AttackSpec(_FrozenModel):
     crit_range: int = Field(default=20, ge=2, le=20)
     crit_mult: int = Field(default=2, ge=2, le=4)
     reach_ft: int = 5
+    reach_weapon: bool = False
     range_increment_ft: int | None = None
     count: int = Field(default=1, ge=1)
     firearm: bool = False