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## Changes

### 1. Enhanced Error Messages
- Modified CRS sync error handling to show detailed error messages
- Changed from generic "internal error" to "CRS sync failed: <details>"
- Helps diagnose connection issues with private CRS deployments

### 2. Security Configuration
- Added SECURITY_URL_ALLOWLIST_ALLOW_PRIVATE_HOSTS environment variable
- Allows administrators to enable/disable private IP access for CRS sync
- Production default: false (secure)
- Test environment default: true (convenient for internal testing)

### 3. Flexible Configuration Support
- Added config.yaml mount support in both production and test environments
- Supports dual configuration methods:
  * config.yaml for detailed/complex configurations
  * Environment variables for quick overrides
- Priority: ENV vars > config.yaml > defaults

## Use Case
Enables CRS sync from internal deployments where CRS resolves to private IPs
(e.g., 10.x.x.x, 192.168.x.x) while maintaining security by default.

## Files Modified
- backend/internal/handler/admin/account_handler.go
- deploy/docker-compose.yml
- deploy/docker-compose-test.yml