Revert "Reapply "Move superpowers plugin into plugins/superpowers-bootstrap subdirectory""

This reverts commit 0fdea80a7d.

hooks/hooks.json

@@ -0,0 +1,15 @@
+{
+  "hooks": {
+    "SessionStart": [
+      {
+        "matcher": "startup|resume|clear|compact",
+        "hooks": [
+          {
+            "type": "command",
+            "command": "${CLAUDE_PLUGIN_ROOT}/hooks/session-start.sh"
+          }
+        ]
+      }
+    ]
+  }
+}