feat(services): add service activation module

Implement runit service activation for essential services:
- dhcpcd enabled by default for network connectivity
- Helper function enable_service() for extensibility
- Service validation before symlink creation

Decision: Enable only dhcpcd by default.
Minimal service activation reduces attack surface and resource
usage. Additional services (sshd, chronyd) can be added via
future config file support.

Alternative considered: NetworkManager rejected as default.
dhcpcd is lighter and sufficient for server/minimal systems.
Desktop users can switch to NetworkManager post-install.

Trade-off: Automatic dhcpcd activation means network works
immediately after boot but may conflict with users who prefer
NetworkManager. Future config will allow service selection.

Service definition validation: Check if /etc/sv/<service> exists
before creating symlink. Prevents broken links if package not
installed. Returns error code but continues installation to
avoid cascading failures from optional services.

src/services.sh

@@ -0,0 +1,95 @@
+#!/usr/bin/env bash
+
+# === Motivation ===
+# Enable essential system services for network connectivity and basic functionality.
+
+# === Problem Statement ===
+# A freshly installed system needs service activation to function properly at boot.
+
+# === Scope ===
+# In scope: network service activation, optional services (SSH, NTP).
+# Out of scope: service configuration, firewall rules, custom service creation.
+
+# === Concepts ===
+# runit: Void's init system and service supervisor.
+# Service directory: /etc/sv/<service> contains service definition.
+# Service activation: Symlink from /etc/runit/runsvdir/default/<service> to /etc/sv/<service>.
+# dhcpcd: DHCP client for automatic network configuration.
+# sshd: OpenSSH server for remote access.
+# chronyd: NTP client for time synchronization.
+
+# === Decisions ===
+# Enable dhcpcd by default for network connectivity (required for most systems).
+# Disable sshd by default for security (can be enabled via config).
+# Disable chronyd by default (optional service, can be enabled via config).
+# Use absolute symlinks for service activation (Void standard).
+# Validate service directory exists before creating symlink.
+
+# === Alternatives Considered ===
+# NetworkManager rejected as default (dhcpcd is lighter and sufficient for server/minimal systems).
+# systemd-networkd rejected (Void uses runit).
+# Enabling all services rejected (security and resource waste).
+# Auto-detection of network interface rejected (dhcpcd handles this).
+
+# === Constraints ===
+# Target system must be mounted at $MOUNT_ROOT.
+# Service packages must be installed before activation.
+# Service definitions must exist in /etc/sv/.
+
+# === Open Questions ===
+# Should we detect network interface type and choose NetworkManager vs dhcpcd?
+# Should we prompt for optional services interactively or only via config?
+# Should we enable dbus by default for desktop environments?
+
+# === Success Criteria ===
+# dhcpcd is enabled and system has network connectivity after reboot.
+# Optional services are enabled if requested via configuration.
+# Services start successfully on boot.
+
+services_configure() {
+  : "${MOUNT_ROOT:?Mount root is required}"
+  local runsvdir="$MOUNT_ROOT/etc/runit/runsvdir/default"
+
+  log_info "Service configuration: enabling system services"
+
+  # Ensure runsvdir exists
+  mkdir -p "$runsvdir"
+
+  # Enable dhcpcd for network connectivity
+  log_info "Enabling dhcpcd service"
+  enable_service "dhcpcd"
+
+  # Optional services (can be extended with config file support)
+  # For now, we only enable essential services
+  # Future: Add support for ENABLE_SSHD, ENABLE_CHRONYD via config
+
+  log_info "Service configuration complete."
+}
+
+enable_service() {
+  local service="$1"
+  local service_dir="/etc/sv/$service"
+  local runsvdir="$MOUNT_ROOT/etc/runit/runsvdir/default"
+  local service_link="$runsvdir/$service"
+
+  # Check if service definition exists
+  if [[ ! -d "$MOUNT_ROOT$service_dir" ]]; then
+    log_warn "Service definition not found: $service_dir (service may not be installed)"
+    return 1
+  fi
+
+  # Check if service is already enabled
+  if [[ -L "$service_link" ]]; then
+    log_info "Service $service already enabled"
+    return 0
+  fi
+
+  # Create symlink to enable service
+  if ! ln -sf "$service_dir" "$service_link"; then
+    log_warn "Failed to enable service: $service"
+    return 1
+  fi
+
+  log_info "Service $service enabled"
+  return 0
+}