feat(13-01): add InterfaceInfo collector with MAC lowercasing and tests

- InterfaceInfo struct for link discovery (name, mac, type, running)
- CollectInterfaceInfo runs /interface/print (version-agnostic)
- MAC addresses lowercased for consistent matching
- Entries without mac-address skipped (loopback, bridge)
- Preserved existing InterfaceStats traffic counter collector

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

poller/internal/device/interfaces.go

@@ -1,10 +1,10 @@
-// Package device provides RouterOS metric collectors for the poller.
 package device
 
 import (
 	"fmt"
 	"log/slog"
 	"strconv"
+	"strings"
 
 	routeros "github.com/go-routeros/routeros/v3"
 )
@@ -59,3 +59,65 @@ func CollectInterfaces(client *routeros.Client) ([]InterfaceStats, error) {
 
 	return stats, nil
 }
+
+// InterfaceInfo holds basic interface identity data from a RouterOS device.
+// This is used for link discovery — MAC addresses identify which device owns
+// each end of a network link.
+type InterfaceInfo struct {
+	Name       string `json:"name"`
+	MacAddress string `json:"mac_address"`
+	Type       string `json:"type"`
+	Running    bool   `json:"running"`
+}
+
+// normalizeMACAddress lowercases a MAC address for consistent matching.
+func normalizeMACAddress(mac string) string {
+	return strings.ToLower(mac)
+}
+
+// parseRunning converts a RouterOS "true"/"false" string to a Go bool.
+func parseRunning(s string) bool {
+	return s == "true"
+}
+
+// CollectInterfaceInfo queries the RouterOS device for all interfaces and
+// returns their name, MAC address, type, and running status.
+//
+// The /interface/print command is version-agnostic (works on both v6 and v7).
+// Entries with an empty mac-address (loopback, bridge without MAC) are skipped.
+//
+// Returns nil, nil when the device has no interfaces (matching the
+// CollectWireless pattern — empty result is not an error).
+func CollectInterfaceInfo(client *routeros.Client) ([]InterfaceInfo, error) {
+	reply, err := client.Run("/interface/print")
+	if err != nil {
+		slog.Debug("failed to collect interface info", "error", err)
+		return nil, nil
+	}
+
+	if len(reply.Re) == 0 {
+		return nil, nil
+	}
+
+	result := make([]InterfaceInfo, 0, len(reply.Re))
+	for _, s := range reply.Re {
+		m := s.Map
+		mac := m["mac-address"]
+		if mac == "" {
+			continue
+		}
+
+		result = append(result, InterfaceInfo{
+			Name:       m["name"],
+			MacAddress: normalizeMACAddress(mac),
+			Type:       m["type"],
+			Running:    parseRunning(m["running"]),
+		})
+	}
+
+	if len(result) == 0 {
+		return nil, nil
+	}
+
+	return result, nil
+}