Add stderr test hook for UI experiment

plugin/hooks/hooks.json

@@ -8,6 +8,11 @@
             "type": "command",
             "command": "cd \"${CLAUDE_PLUGIN_ROOT}/..\" && npm install --prefer-offline --no-audit --no-fund --loglevel=silent && node ${CLAUDE_PLUGIN_ROOT}/scripts/context-hook.js",
             "timeout": 300
+          },
+          {
+            "type": "command",
+            "command": "node ${CLAUDE_PLUGIN_ROOT}/scripts/stderr-test-hook.js",
+            "timeout": 10
           }
         ]
       }

plugin/scripts/stderr-test-hook.js

@@ -0,0 +1,3 @@
+#!/usr/bin/env node
+#!/usr/bin/env node
+console.error("\u{1F9EA} TEST: This is a stderr message from the claude-mem hook");process.exit(0);