fix: Move devcontainer to repo root for Codespaces detection

GitHub Codespaces only looks for devcontainer.json in:
- .devcontainer/devcontainer.json
- .devcontainer/<subfolder>/devcontainer.json
- .devcontainer.json

It does NOT look inside project subfolders like autogpt_platform/.devcontainer/

Moved to .devcontainer/platform/ which:
1. Will be detected by Codespaces
2. Allows multiple configs (platform vs classic)
3. Updated all path references accordingly

.devcontainer/platform/scripts/poststart.sh

@@ -0,0 +1,44 @@
+#!/bin/bash
+# =============================================================================
+# POSTSTART SCRIPT - Runs every time the codespace starts
+# =============================================================================
+# This script runs when:
+# 1. Codespace is first created (after postcreate)
+# 2. Codespace resumes from stopped state
+# 3. Codespace rebuilds
+#
+# It ensures dependency services are running. Backend/Frontend are run
+# manually by the developer for hot-reload during development.
+# =============================================================================
+
+echo "🔄 Starting dependency services..."
+
+cd /workspaces/AutoGPT/autogpt_platform
+
+# Ensure Docker socket is available
+if [ -e /var/run/docker-host.sock ]; then
+    sudo ln -sf /var/run/docker-host.sock /var/run/docker.sock 2>/dev/null || true
+fi
+
+# Wait for Docker
+timeout 30 bash -c 'until docker info &>/dev/null; do sleep 1; done' || {
+    echo "⚠️ Docker not available, services may need manual start"
+    exit 0
+}
+
+# Start only dependency services (not backend/frontend)
+docker compose up -d db redis rabbitmq kong auth
+
+# Quick health check
+echo "⏳ Waiting for services..."
+sleep 5
+
+if docker compose ps | grep -q "running"; then
+    echo "✅ Dependency services are running"
+    echo ""
+    echo "🚀 Start development with:"
+    echo "   make run-backend   # Terminal 1"
+    echo "   make run-frontend  # Terminal 2"
+else
+    echo "⚠️ Some services may not be running. Try: docker compose up -d"
+fi