adventure: T6 Inversion Stitch (Seamstress) + boss re-strengthen (P8)

Second in-combat Layer-2 mechanic, reusing Amendment's round-end seam. In the
Seamstress's phase 2 (<=35% HP) the room sews inside-out in a repeating
warn(1)->sting(2) cadence, telegraphed one round ahead: during a pulse player
heals (self + ally) invert to damage, floored at 1 HP. State
inversionActive/inversionTelegraph round-trips through CombatStatuses so a
suspend/resume can't drop or double a pulse.

Sim surfaced that unplace is reach-bound (only ~37% reach the boss, then cleared
her ~98%), so the mechanic alone is sub-noise. Re-strengthened the Seamstress,
the weakest T6 boss (over-softened by P7 for a zone lift that never came):
HP 385->460, Atk 39->45, Needle Rain proc 0.40->0.45. Sim-validated at
fighter zone 37.5% (in range), and a real boss fight now instead of a victory lap.

Claude-Session: https://claude.ai/code/session_0156WqjgsbmSY2U8eQ3Kkb1s

internal/plugin/postgame_bestiary.go

@@ -167,9 +167,9 @@ var _ = func() bool {
 		},
 		"boss_seamstress": {
 			ID: "boss_seamstress", Name: "The Seamstress",
-			CR: 27, HP: 385, AC: 21, Attack: 39, AttackBonus: 12, Speed: 14,
+			CR: 27, HP: 460, AC: 21, Attack: 45, AttackBonus: 12, Speed: 14,
 			BlockRate: 0.15,
-			Ability:   &MonsterAbility{Name: "Needle Rain", Phase: "decisive", ProcChance: 0.40, Effect: "aoe"},
+			Ability:   &MonsterAbility{Name: "Needle Rain", Phase: "decisive", ProcChance: 0.45, Effect: "aoe"},
 			XPValue:   100000,
 			Notes:     "Unplace boss. A corrupted celestial sewing herself into the tear; half of her is on the other side. Phase 2 below 35% HP. (Layer 2: Inversion Stitch — healing and damage swap direction on her in telegraphed pulses.)",
 		},