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/oncreate.sh

@@ -0,0 +1,133 @@
+#!/bin/bash
+# =============================================================================
+# ONCREATE SCRIPT - Runs during prebuild
+# =============================================================================
+# This script runs during the prebuild phase (GitHub Actions).
+# It caches everything that's safe to cache:
+#   ✅ Dependency Docker images (postgres, redis, rabbitmq, etc.)
+#   ✅ Python packages (poetry install)
+#   ✅ Node packages (pnpm install)
+#
+# It does NOT build backend/frontend Docker images because those would
+# contain stale code from the prebuild branch, not the PR being reviewed.
+# =============================================================================
+
+set -e  # Exit on error
+set -x  # Print commands for debugging
+
+echo "🚀 Starting prebuild setup..."
+
+# Workspace is autogpt_platform
+cd /workspaces/AutoGPT/autogpt_platform
+
+# =============================================================================
+# Install Backend Dependencies
+# =============================================================================
+echo "📦 Installing backend dependencies..."
+
+cd backend
+
+# Install Poetry if not present
+if ! command -v poetry &> /dev/null; then
+    echo "Installing Poetry..."
+    curl -sSL https://install.python-poetry.org | python3 -
+    export PATH="$HOME/.local/bin:$PATH"
+fi
+
+# Install Python dependencies
+poetry install --no-interaction --no-ansi
+
+# Generate Prisma client (schema only, no DB needed)
+echo "🔧 Generating Prisma client..."
+poetry run prisma generate || true
+poetry run gen-prisma-stub || true
+
+cd ..
+
+# =============================================================================
+# Install Frontend Dependencies
+# =============================================================================
+echo "📦 Installing frontend dependencies..."
+
+cd frontend
+
+# Install pnpm if not present
+if ! command -v pnpm &> /dev/null; then
+    echo "Installing pnpm..."
+    npm install -g pnpm
+fi
+
+# Install Node dependencies
+pnpm install --frozen-lockfile
+
+cd ..
+
+# =============================================================================
+# Pull Dependency Docker Images ONLY
+# =============================================================================
+# We only pull infrastructure images. Backend/Frontend run natively
+# to ensure we always use the current branch's code.
+# =============================================================================
+echo "🐳 Pulling dependency Docker images..."
+
+# Start Docker daemon if using docker-in-docker
+if [ -e /var/run/docker-host.sock ]; then
+    sudo ln -sf /var/run/docker-host.sock /var/run/docker.sock || true
+fi
+
+# Pull dependency images in parallel
+docker pull supabase/gotrue:v2.170.0 &
+docker pull supabase/studio:20250224-d10db0f &
+docker pull kong:2.8.1 &
+docker pull supabase/postgres:15.8.1.060 &
+docker pull redis:latest &
+docker pull rabbitmq:management &
+
+# Wait for all pulls to complete
+wait
+
+echo "✅ Dependency images pulled"
+
+# NOTE: We intentionally do NOT build backend/frontend images here.
+# Those need to use the current branch's code, not prebuild's code.
+
+# =============================================================================
+# Copy environment files
+# =============================================================================
+echo "📄 Setting up environment files..."
+
+cd /workspaces/AutoGPT/autogpt_platform
+
+# Backend
+if [ ! -f backend/.env ]; then
+    cp backend/.env.default backend/.env
+fi
+
+# Frontend
+if [ ! -f frontend/.env ]; then
+    cp frontend/.env.default frontend/.env
+fi
+
+# Platform root
+if [ ! -f .env ]; then
+    cp .env.default .env
+fi
+
+# =============================================================================
+# Done!
+# =============================================================================
+echo ""
+echo "=============================================="
+echo "✅ PREBUILD COMPLETE"
+echo "=============================================="
+echo ""
+echo "Cached:"
+echo "  ✅ Python packages (poetry)"
+echo "  ✅ Node packages (pnpm)"
+echo "  ✅ Dependency Docker images"
+echo ""
+echo "NOT cached (intentionally):"
+echo "  ❌ Backend/Frontend containers (would have stale code)"
+echo ""
+echo "The postcreate script will start services."
+echo ""