docs: add architecture awareness system — CLAUDE.md §13/§14 + ARCHITECTURE_BRIEF

- Activate CLAUDE.md with §13 architecture snapshot (auto-sync markers)
  and §14 anti-pattern warnings + scenario instructions
- Fix dead link to non-existent STABILIZATION_DIRECTIVE.md
- Update stale numbers (93→130 SaaS APIs, 171→182 Tauri commands, 13→15 admin pages)
- Create docs/ARCHITECTURE_BRIEF.md as permanent architecture reference
  covering 10 subsystems (butler, chatstream, LLM drivers, client routing,
  SaaS auth, memory pipeline, Pipeline DSL, Hands, middleware, key paths)
- Add /sync-arch skill for manual or workflow-triggered architecture sync
- Add PostToolUse hook to remind doc sync after git commit/push
- Update §8.3 completion flow to include architecture snapshot updates
- Mark memory files (system_architecture, butler_mode) as migrated to BRIEF
- Add ARCHITECTURE_BRIEF.md as top entry in MEMORY.md index

.claude/settings.json

@@ -0,0 +1,15 @@
+{
+  "hooks": {
+    "PostToolUse": [
+      {
+        "matcher": "Bash",
+        "hooks": [
+          {
+            "type": "command",
+            "command": "node .claude/hooks/arch-sync-check.js"
+          }
+        ]
+      }
+    ]
+  }
+}