Rename stderr-test-hook to user-message-hook for production

Changes:
- Renamed src/hooks/stderr-test-hook.ts to user-message-hook.ts
- Updated user-message-hook with production-ready messaging
- Updated scripts/build-hooks.js to build user-message-hook
- Updated plugin/hooks/hooks.json to reference user-message-hook.js
- Cleaned up old stderr-test-hook.js files
- Built and deployed user-message-hook.js to plugin directory

This hook displays context information to users via stderr, which is
currently the only way to show messages in Claude Code UI. It runs in
parallel with context-hook during SessionStart.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

plugin/scripts/user-message-hook.js

@@ -0,0 +1,7 @@
+#!/usr/bin/env node
+import{execSync as e}from"child_process";try{let o=e("node ~/.claude/plugins/marketplaces/thedotmack/plugin/scripts/context-hook.js --colors",{encoding:"utf8"});console.error(`
+
+\u{1F4DD} Claude-Mem Context Loaded
+   \u2139\uFE0F  Note: This appears as stderr but is informational only
+
+`+o)}catch(o){console.error(`\u274C Failed to load context display: ${o}`)}process.exit(3);