fix(models): require a positive range_increment_ft (reject 0 and negatives)

src/pf1e_simulator/models.py

@@ -278,7 +278,11 @@ class AttackSpec(_FrozenModel):
     crit_mult: int = Field(default=2, ge=2, le=4)
     reach_ft: int = 5
     reach_weapon: bool = False
-    range_increment_ft: int | None = None
+    # Positive or None (None = no range increments: melee, or touch at natural
+    # reach). A zero increment would crash the engine's range_penalty with a
+    # ZeroDivisionError (dist_ft // 0); a negative one silently makes the
+    # weapon unusable -- both are data errors, rejected at the schema.
+    range_increment_ft: int | None = Field(default=None, ge=1)
     count: int = Field(default=1, ge=1)
     firearm: bool = False
     two_handed: bool = False