feat(platform/docker): add frontend service to docker-compose with env config improvements (#10615)

## 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, unified .env file support, 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

### 📁 Unified .env File Support
- **Frontend .env loading**: Automatically loads `.env` file during
Docker build and runtime
- **Backend .env loading**: Optional `.env` file support with fallback
to sensible defaults in `settings.py`
- **Single source of truth**: All `NEXT_PUBLIC_*` and API keys can be
defined in respective `.env` files
- **Docker integration**: Updated `.dockerignore` to include `.env`
files in build context
- **Git tracking**: Frontend and backend `.env` files are now trackable
(removed from gitignore)

### 🔧 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
- **Shared backend variables**: Common environment variables (service
hosts, auth settings) centralized using YAML anchors

### 🛠️ 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
- **Settings.py improvements**: Better defaults for CORS origins and
optional .env file loading

### 🔗 Files Changed
- `docker-compose.yml` & `docker-compose.platform.yml` - Added frontend
service and shared backend env vars
- `frontend/Dockerfile` - Simplified build process to use .env files
directly
- `backend/settings.py` - Optional .env loading and better defaults
- `frontend/src/lib/env-config.ts` - New centralized environment
configuration
- `.dockerignore` - Allow .env files in build context
- `.gitignore` - Updated to allow frontend/backend .env files
- Multiple frontend files - Updated to use env helpers
- Updates to both auto installer scripts to work with the latest setup!

## 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
with .env files
- ✅ **Development friendly**: Works in both Docker and local development
- ✅ **API key management**: Easy configuration through .env files for
all services
- ✅ **No more manual env vars**: Frontend and backend automatically load
their respective .env files

## 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
- ✅ .env file loading works correctly in both build and runtime phases
- ✅ Backend services work with and without .env files present

### Checklist 📋

#### For configuration changes:
- [x] `.env.default` is updated or already compatible with my changes
- [x] `docker-compose.yml` is updated or already compatible with my
changes
- [x] I have included a list of my configuration changes in the PR
description (under **Changes**)

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

---------

Co-authored-by: Lluis Agusti <[email protected]>
Co-authored-by: Claude <[email protected]>
Co-authored-by: Nicholas Tindle <[email protected]>
Co-authored-by: Claude <[email protected]>
Co-authored-by: Bentlybro <[email protected]>