Adv 2.0 D&D Phase 10 SUB2a-ii: Battle Master + Assassin L5/L7

Battle Master:
  - New "superiority" resource pool (4/long-rest at L5), provisioned via
    initSubclassResources at !subclass selection.
  - Three armed maneuvers fueled by superiority dice:
    * Precision Attack — +d8 (≈+4) to first attack roll
    * Tripping Attack  — enemy skips first attack (reuses Phase 9
      SpellEnemySkipFirst)
    * Rally            — +(d8 + CHA) HealItem at <50% HP
  - L7 Know Your Enemy proxied as +1 AttackBonus passive.

Assassin:
  - L5 Assassinate: AssassinateAdvantage (re-roll first miss, take better
    of two d20s) + AssassinateBonusDmg = level (5 at L5) stacked on top
    of the Rogue's existing Sneak Attack auto-crit.
  - L7 Impostor bumps the bonus damage by +3.
  - L5 Infiltration Expertise → +5 Deception; L7 Impostor → +10.

Engine:
  - CombatModifiers gains FirstAttackBonus, AssassinateAdvantage,
    AssassinateBonusDmg.
  - resolvePlayerAttack consumes each on the first attack only via new
    combatState one-shot flags.

Tests added: 14 covering passive gating (BM L7+, Assassin L5/L7),
maneuver Apply flags, superiority pool init for BM only, !arm gating
across class/subclass for precision_attack, Deception bonus tiers,
statistical lift from FirstAttackBonus and AssassinateBonusDmg in
SimulateCombat.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

internal/plugin/dnd_skills.go

@@ -163,6 +163,18 @@ func subclassSkillBonus(c *DnDCharacter, info dndSkillInfo) int {
 		if c.Level >= 5 && info.Key == SkillSleightOfHand {
 			return 5
 		}
+	case SubclassAssassin:
+		// L5 Infiltration Expertise: crafting a false identity is a
+		// Deception skill workout. L7 Impostor — perfect mimicry of voice
+		// and manner — bumps the bonus further.
+		if info.Key == SkillDeception {
+			if c.Level >= 7 {
+				return 10
+			}
+			if c.Level >= 5 {
+				return 5
+			}
+		}
 	}
 	return 0
 }