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_subclass_cmd.go

@@ -119,6 +119,11 @@ func (p *AdventurePlugin) applySubclassChoice(
 	if err := SaveDnDCharacter(c); err != nil {
 		return p.SendDM(ctx.Sender, "Couldn't save subclass choice: "+err.Error())
 	}
+	// Phase 10 SUB2a-ii — provision subclass-specific resource pools (e.g.
+	// Battle Master superiority dice). Idempotent. Failure is non-fatal —
+	// the player still gets the subclass; resources can be re-initialized
+	// next long rest.
+	_ = initSubclassResources(ctx.Sender, chosen)
 	if charged {
 		// Debit last; race vs. balance change is rare and strictly safer
 		// to favor the player than risk taking euros without applying the