Add GET /api/v1/probe endpoint for device inspection

Fast (~1-3s) endpoint that gathers network info about a device
before full stream discovery. Runs ping first, then parallel probes.

Features:
- Ping with ICMP + TCP fallback (works without root)
- Reverse DNS hostname lookup
- ARP table MAC address + OUI vendor identification (2403 entries, 51 camera vendors)
- mDNS HomeKit detection (camera/doorbell, paired status)
- Extensible Prober interface for adding new probe types
- 3-second overall timeout, parallel execution

Response includes "type" field:
- "unreachable" - device not responding
- "standard" - normal IP camera (RTSP/HTTP/ONVIF flow)
- "homekit" - Apple HomeKit camera (PIN pairing flow)

internal/camera/discovery/prober_arp.go

@@ -0,0 +1,80 @@
+package discovery
+
+import (
+	"bufio"
+	"context"
+	"fmt"
+	"os"
+	"strings"
+
+	"github.com/eduard256/Strix/internal/models"
+)
+
+// ARPProber looks up the MAC address from the system ARP table
+// and resolves it to a vendor name using the OUI database.
+type ARPProber struct {
+	ouiDB *OUIDatabase
+}
+
+// NewARPProber creates a new ARP prober with the given OUI database.
+func NewARPProber(ouiDB *OUIDatabase) *ARPProber {
+	return &ARPProber{ouiDB: ouiDB}
+}
+
+func (p *ARPProber) Name() string { return "arp" }
+
+// Probe looks up the MAC address for the given IP in the ARP table.
+// Returns nil if the IP is not in the ARP table (e.g., different subnet, VPN).
+// This only works on Linux (reads /proc/net/arp).
+func (p *ARPProber) Probe(ctx context.Context, ip string) (any, error) {
+	mac, err := p.lookupARP(ip)
+	if err != nil || mac == "" {
+		return nil, nil // Not in ARP table is not an error
+	}
+
+	vendor := ""
+	if p.ouiDB != nil {
+		vendor = p.ouiDB.LookupVendor(mac)
+	}
+
+	return &models.ARPProbeResult{
+		MAC:    mac,
+		Vendor: vendor,
+	}, nil
+}
+
+// lookupARP reads /proc/net/arp to find the MAC address for the given IP.
+//
+// Format of /proc/net/arp:
+//
+//	IP address       HW type     Flags       HW address            Mask     Device
+//	192.168.1.1      0x1         0x2         aa:bb:cc:dd:ee:ff     *        eth0
+func (p *ARPProber) lookupARP(ip string) (string, error) {
+	file, err := os.Open("/proc/net/arp")
+	if err != nil {
+		return "", fmt.Errorf("failed to open ARP table: %w", err)
+	}
+	defer file.Close()
+
+	scanner := bufio.NewScanner(file)
+	scanner.Scan() // Skip header line
+
+	for scanner.Scan() {
+		fields := strings.Fields(scanner.Text())
+		if len(fields) < 4 {
+			continue
+		}
+
+		// fields[0] = IP address, fields[3] = HW address
+		if fields[0] == ip {
+			mac := fields[3]
+			// "00:00:00:00:00:00" means incomplete ARP entry
+			if mac == "00:00:00:00:00:00" {
+				return "", nil
+			}
+			return strings.ToUpper(mac), nil
+		}
+	}
+
+	return "", nil
+}