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/docker-compose.devcontainer.yml

@@ -0,0 +1,56 @@
+# Docker Compose override for dev container
+# This extends the main autogpt_platform/docker-compose.yml
+
+services:
+  devcontainer:
+    image: mcr.microsoft.com/devcontainers/base:ubuntu-24.04
+    volumes:
+      # Mount the entire AutoGPT repo
+      - ../..:/workspaces/AutoGPT:cached
+      # Docker-in-Docker socket
+      - /var/run/docker.sock:/var/run/docker-host.sock
+    
+    # Keep container running
+    command: sleep infinity
+    
+    # Use host network for easy access to other services
+    network_mode: host
+    
+    environment:
+      # Codespaces detection
+      - CODESPACES=true
+      
+      # Database - use localhost (host network mode)
+      - DATABASE_URL=postgresql://postgres:your-super-secret-and-long-postgres-password@localhost:5432/postgres?schema=platform&connect_timeout=60
+      - DIRECT_URL=postgresql://postgres:your-super-secret-and-long-postgres-password@localhost:5432/postgres?schema=platform&connect_timeout=60
+      - DB_HOST=localhost
+      - DB_PORT=5432
+      
+      # Redis
+      - REDIS_HOST=localhost
+      - REDIS_PORT=6379
+      
+      # RabbitMQ
+      - RABBITMQ_HOST=localhost
+      
+      # Supabase
+      - SUPABASE_URL=http://localhost:8000
+      - SUPABASE_SERVICE_ROLE_KEY=eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyAgCiAgICAicm9sZSI6ICJzZXJ2aWNlX3JvbGUiLAogICAgImlzcyI6ICJzdXBhYmFzZS1kZW1vIiwKICAgICJpYXQiOiAxNjQxNzY5MjAwLAogICAgImV4cCI6IDE3OTk1MzU2MDAKfQ.DaYlNEoUrrEn2Ig7tqibS-PHK5vgusbcbo7X36XVt4Q
+      - JWT_VERIFY_KEY=your-super-secret-jwt-token-with-at-least-32-characters-long
+      
+      # Frontend URLs
+      - NEXT_PUBLIC_SUPABASE_URL=http://localhost:8000
+      - NEXT_PUBLIC_AGPT_SERVER_URL=http://localhost:8006/api
+      - NEXT_PUBLIC_AGPT_WS_SERVER_URL=ws://localhost:8001/ws
+      
+      # Backend URLs
+      - PLATFORM_BASE_URL=http://localhost:8000
+      - FRONTEND_BASE_URL=http://localhost:3000
+      
+      # Disable telemetry in dev
+      - NEXT_TELEMETRY_DISABLED=1
+      - DO_NOT_TRACK=1
+      
+      # Poetry
+      - POETRY_VIRTUALENVS_IN_PROJECT=true
+      - POETRY_NO_INTERACTION=1