feat(deployment): replace monster scripts with modular helper scripts (#87)

- Add install.sh orchestrator with upgrade support
- Add 6 helper scripts (<100 lines each) replacing 700-800 line monsters
- Add deployment/linux/furt.service systemd template
- Support both fresh install and upgrade modes
- Platform-aware detection (OpenBSD/FreeBSD vs Linux)
- Skip user/service creation in upgrade mode
- Preserve existing configuration during updates
- Remove merkwerk dependency from production install script

Helper scripts:
- scripts/setup-user.sh - Create system user (_furt/furt)
- scripts/setup-directories.sh - Create directory structure
- scripts/sync-files.sh - Copy source files to installation
- scripts/create-service.sh - Create system service from templates
- scripts/validate-config.sh - Validate furt.conf syntax
- scripts/health-check.sh - Basic health check functionality

Closes DAW/furt#87

scripts/validate-config.sh

@@ -0,0 +1,49 @@
+#!/bin/sh
+# scripts/validate-config.sh - Validate furt configuration
+
+set -e
+
+# Detect config file location
+if [ "$(uname)" = "OpenBSD" ] || [ "$(uname)" = "FreeBSD" ]; then
+    CONFIG_FILE="/usr/local/etc/furt/furt.conf"
+else
+    CONFIG_FILE="/etc/furt/furt.conf"
+fi
+
+echo "Validating configuration: $CONFIG_FILE"
+
+# Check if config file exists
+if [ ! -f "$CONFIG_FILE" ]; then
+    echo "Error: Configuration file not found: $CONFIG_FILE"
+    exit 1
+fi
+
+# Basic INI syntax validation
+if ! grep -q '^\[server\]' "$CONFIG_FILE"; then
+    echo "Error: [server] section missing in config"
+    exit 1
+fi
+
+if ! grep -q '^port\s*=' "$CONFIG_FILE"; then
+    echo "Error: server port not configured"
+    exit 1
+fi
+
+if ! grep -q '^host\s*=' "$CONFIG_FILE"; then
+    echo "Error: server host not configured"
+    exit 1
+fi
+
+# Check for at least one API key
+if ! grep -q '^\[api_key' "$CONFIG_FILE"; then
+    echo "Warning: No API keys configured"
+fi
+
+# Check permissions (should not be world-readable due to secrets)
+PERMS=$(stat -c '%a' "$CONFIG_FILE" 2>/dev/null || stat -f '%Lp' "$CONFIG_FILE")
+if [ "$PERMS" -gt 640 ]; then
+    echo "Warning: Config file permissions too open ($PERMS), should be 640"
+fi
+
+echo "Configuration validation completed"
+