Add notification hook, directory CLAUDE.md scaffolding

- Wire Notification event in settings.json to new notify.sh hook
- notify.sh: Windows toast notifications via PowerShell balloon tip
- docs/CLAUDE.md: authoring standards for ADRs, TR registry, control manifest, engine reference
- design/CLAUDE.md: GDD directory guidance placeholder
- src/: scaffold with .gitkeep and CLAUDE.md authoring guide

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

.claude/settings.json

@@ -83,6 +83,18 @@
         ]
       }
     ],
+    "Notification": [
+      {
+        "matcher": "",
+        "hooks": [
+          {
+            "type": "command",
+            "command": "bash .claude/hooks/notify.sh",
+            "timeout": 10
+          }
+        ]
+      }
+    ],
     "PreCompact": [
       {
         "matcher": "",