feat(docker): add frontend service to docker-compose with env config improvements (#10536)

## Summary
This PR adds the frontend service to the Docker Compose configuration,
enabling `docker compose up` to run the complete stack including the
frontend. It also implements comprehensive environment variable
improvements and fixes Docker networking issues.

## Key Changes

### 🐳 Docker Compose Improvements
- **Added frontend service** to `docker-compose.yml` and
`docker-compose.platform.yml`
- **Production build**: Uses `pnpm build + serve` instead of dev server
for better stability and lower memory usage
- **Service dependencies**: Frontend now waits for backend services
(`rest_server`, `websocket_server`) to be ready
- **YAML anchors**: Implemented DRY configuration to avoid duplicating
environment values

### 🔧 Environment Variable Architecture
- **Dual environment strategy**: 
- Server-side code uses Docker service names
(`http://rest_server:8006/api`)
  - Client-side code uses localhost URLs (`http://localhost:8006/api`)
- **Comprehensive config**: Added build args and runtime environment
variables
- **Network compatibility**: Fixes connection issues between frontend
and backend containers

### 🛠️ Code Improvements
- **Centralized env-config helper** (`/frontend/src/lib/env-config.ts`)
with server-side priority
- **Updated all frontend code** to use shared environment helpers
instead of direct `process.env` access
- **Consistent API**: All environment variable access now goes through
helper functions

### 🔗 Files Changed
- `docker-compose.yml` & `docker-compose.platform.yml` - Added frontend
service
- `frontend/Dockerfile` - Added build args for environment variables
- `frontend/src/lib/env-config.ts` - New centralized environment
configuration
- Multiple frontend files - Updated to use env helpers

## Benefits
- ✅ **Single command deployment**: `docker compose up` now runs
everything
- ✅ **Better reliability**: Production build reduces memory usage and
crashes
- ✅ **Network compatibility**: Proper container-to-container
communication
- ✅ **Maintainable config**: Centralized environment variable management
- ✅ **Development friendly**: Works in both Docker and local development

## Testing
- ✅ Verified Docker service communication works correctly
- ✅ Frontend responds and serves content properly  
- ✅ Environment variables are correctly resolved in both server and
client contexts
- ✅ No connection errors after implementing service dependencies

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

---------

Co-authored-by: Claude <noreply@anthropic.com>

autogpt_platform/frontend/src/app/api/proxy/[...path]/route.ts

@@ -3,14 +3,11 @@ import {
   makeAuthenticatedFileUpload,
   makeAuthenticatedRequest,
 } from "@/lib/autogpt-server-api/helpers";
+import { getAgptServerUrl } from "@/lib/env-config";
 import { NextRequest, NextResponse } from "next/server";
 
 function getBackendBaseUrl() {
-  if (process.env.NEXT_PUBLIC_AGPT_SERVER_URL) {
-    return process.env.NEXT_PUBLIC_AGPT_SERVER_URL.replace("/api", "");
-  }
-
-  return "http://localhost:8006";
+  return getAgptServerUrl().replace("/api", "");
 }
 
 function buildBackendUrl(path: string[], queryString: string): string {