Add explanatory comments for variable overwrites and code flow decisions

This commit adds detailed explanatory comments throughout the codebase to explain
WHY certain logic is needed, not just WHAT the code does. This improves code
maintainability and helps developers understand the reasoning behind complex
decisions.

Key improvements:
- Version string processing: Explain why "v" prefix is added for semantic versioning
- Control-D configuration: Explain why config is reset to prevent mixing of settings
- DNS server categorization: Explain LAN vs public server handling for performance
- Listener configuration: Document complex fallback logic for port/IP selection
- MAC address normalization: Explain cross-platform compatibility needs
- IPv6 address processing: Document Unix-specific interface suffix handling
- Log content truncation: Explain why large content is limited to prevent flooding
- IP address categorization: Document RFC1918 prioritization logic
- IPv4/IPv6 separation: Explain network stack compatibility needs
- DNS priority logic: Document different priority levels for different scenarios
- Domain controller processing: Explain Windows API prefix handling
- Reverse mapping creation: Document API encoding/decoding needs
- Default value fallbacks: Explain why defaults prevent system failures
- IP stack configuration: Document different defaults for different upstream types

These comments help future developers understand the reasoning behind complex
business logic, making the codebase more maintainable and reducing the risk of
incorrect modifications during maintenance.

internal/clientinfo/ndp.go

@@ -174,6 +174,9 @@ func (nd *ndpDiscover) scanUnix(r io.Reader) {
 		}
 		if mac := parseMAC(fields[1]); mac != "" {
 			ip := fields[0]
+			// Remove interface suffix from IPv6 addresses
+			// Unix systems append interface names to IPv6 addresses (e.g., "fe80::1%eth0")
+			// This suffix needs to be removed for proper IP parsing
 			if idx := strings.IndexByte(ip, '%'); idx != -1 {
 				ip = ip[:idx]
 			}
@@ -192,11 +195,15 @@ func normalizeMac(mac string) string {
 		return mac
 	}
 	// Windows use "-" instead of ":" as separator.
+	// This normalization is needed because different operating systems use different
+	// separators for MAC addresses, but net.ParseMAC expects ":" format
 	mac = strings.ReplaceAll(mac, "-", ":")
 	parts := strings.Split(mac, ":")
 	if len(parts) != 6 {
 		return ""
 	}
+	// Pad single-digit hex values with leading zero
+	// This ensures consistent formatting for MAC address parsing
 	for i, c := range parts {
 		if len(c) == 1 {
 			parts[i] = "0" + c