Improve devcontainer configuration

- Simplify Dockerfile: use golang:1.24 base, install Node via features
- Add proper port forwarding for Pulse (7655 frontend, 7656 API)
- Add Vue Volar extension for frontend development
- Add start-pulse-dev.sh helper script for auto-starting dev server
- Add FRONTEND_DEV_HOST to containerEnv for proper binding
- Add .env.devcontainer to .gitignore (local override file)
- Update frontend dependencies

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

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

.devcontainer/start-pulse-dev.sh

@@ -0,0 +1,20 @@
+#!/bin/bash
+# Auto-start script for pulse dev environment
+
+PIDFILE="/tmp/pulse-dev.pid"
+LOGFILE="/tmp/pulse-dev.log"
+
+# Check if already running
+if [ -f "$PIDFILE" ] && kill -0 $(cat "$PIDFILE") 2>/dev/null; then
+    echo "Pulse dev server already running (PID: $(cat $PIDFILE))"
+    exit 0
+fi
+
+# Start hot-dev.sh
+cd /workspaces/pulse
+nohup ./scripts/hot-dev.sh > "$LOGFILE" 2>&1 &
+echo $! > "$PIDFILE"
+
+echo "Pulse dev server starting... (PID: $(cat $PIDFILE))"
+echo "Logs: tail -f $LOGFILE"
+echo "Frontend will be available at http://localhost:7655"