Add director gates system: shared review checkpoints across all workflow skills

Creates .claude/docs/director-gates.md as a central registry of 18 named gate
prompts (CD-*, TD-*, PR-*, LP-*, QL-*, ND-*, AD-*) covering all 7 production
stages. Skills now reference gate IDs instead of embedding inline director prompts,
eliminating drift when prompts need updating.

Updated 15 skills to use gate IDs: brainstorm, map-systems, design-system,
architecture-decision, create-architecture, create-epics, create-stories,
sprint-plan, milestone-review, playtest-report, prototype, story-done,
gate-check, setup-engine, start.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

.claude/skills/design-system/SKILL.md

@@ -557,6 +557,17 @@ the source of truth). Verify:
 - Dependencies are listed with interfaces
 - Acceptance criteria are testable
 
+### 5a-bis: Creative Director Pillar Review
+
+Before finalizing the GDD, spawn `creative-director` via Task using gate **CD-GDD-ALIGN** (`.claude/docs/director-gates.md`).
+
+Pass: completed GDD file path, game pillars (from `design/gdd/game-concept.md` or `design/gdd/game-pillars.md`), MDA aesthetics target.
+
+Handle verdict per the standard rules in `director-gates.md`. After resolution, record the verdict in the GDD Status header:
+`> **Creative Director Review (CD-GDD-ALIGN)**: APPROVED [date] / CONCERNS (accepted) [date] / REVISED [date]`
+
+---
+
 ### 5b: Update Entity Registry
 
 Scan the completed GDD for cross-system facts that should be registered: