Add structured logging system with color-coded output and file logging (#1321)

## Summary
- Add comprehensive logging system with color-coded log levels ([INFO],
[WARN], [ERROR], [OK])
- Wrap all command executions with `run_cmd()` to capture output and
prevent leaks to stdout
- Add file logging with timestamps (default: `openvpn-install.log`)
- Suppress interactive prompts in auto-install mode for cleaner
CI/scripted usage
- Show log file location hint on errors for easier debugging

## Changes
- **openvpn-install.sh**: New logging functions (`log_info`, `log_warn`,
`log_error`, `log_fatal`, `log_success`, `log_prompt`, `log_header`,
`log_menu`, `run_cmd`), all `echo` statements converted to use logging
functions
- **test/validate-output.sh**: New E2E validator that ensures all script
output uses proper log formatting (catches raw echo leaks)
- **test/server-entrypoint.sh**: Integrates output validation into
Docker tests
- **test/Dockerfile.server**: Copies validation script into container

## Configuration
- `VERBOSE=1` - Show command output in terminal
- `LOG_FILE=path` - Customize log location (default:
`openvpn-install.log`)
- `LOG_FILE=""` - Disable file logging
- `FORCE_COLOR=1` - Force colored output in non-TTY environments

test/server-entrypoint.sh

@@ -14,6 +14,7 @@ echo "TUN device ready"
 
 # Set up environment for auto-install
 export AUTO_INSTALL=y
+export FORCE_COLOR=1
 export APPROVE_INSTALL=y
 export APPROVE_IP=y
 export IPV6_SUPPORT=n
@@ -34,11 +35,24 @@ chmod +x /tmp/openvpn-install.sh
 
 echo "Running OpenVPN install script..."
 # Run in subshell because the script calls 'exit 0' after generating client config
+# Capture output to validate logging format, while still displaying it
 # Use || true to prevent set -e from exiting on failure, then check exit code
-(bash -x /tmp/openvpn-install.sh) && INSTALL_EXIT_CODE=0 || INSTALL_EXIT_CODE=$?
+INSTALL_OUTPUT="/tmp/install-output.log"
+(bash /tmp/openvpn-install.sh) 2>&1 | tee "$INSTALL_OUTPUT"
+INSTALL_EXIT_CODE=${PIPESTATUS[0]}
 
 echo "=== Installation complete (exit code: $INSTALL_EXIT_CODE) ==="
 
+# Validate that all output uses proper logging format (ANSI color codes)
+echo "Validating output format..."
+if /opt/test/validate-output.sh "$INSTALL_OUTPUT"; then
+	echo "PASS: All script output uses proper log formatting"
+else
+	echo "FAIL: Script output contains unformatted lines"
+	echo "This indicates echo statements that should use log_* functions"
+	exit 1
+fi
+
 if [ "$INSTALL_EXIT_CODE" -ne 0 ]; then
 	echo "ERROR: Install script failed with exit code $INSTALL_EXIT_CODE"
 	exit 1