ax(ueps): rename buf→buffer in usage example comments

Abbreviated names in comments teach agents bad patterns.
AX Principle 1 applies to usage examples too.

Co-Authored-By: Charon <charon@lethean.io>

pkg/ueps/packet.go

@@ -8,7 +8,7 @@ import (
 	"io"
 )
 
-// writeTLV(buf, TagPayload, oversized) → errTLVValueTooLarge
+// writeTLV(buffer, TagPayload, oversized) → errTLVValueTooLarge
 // if errors.Is(err, errTLVValueTooLarge) { /* value exceeded 255-byte TLV length limit */ }
 var errTLVValueTooLarge = tlvError("TLV value too large for 1-byte length header")
 
@@ -107,8 +107,8 @@ func (builder *PacketBuilder) MarshalAndSign(sharedSecret []byte) ([]byte, error
 	return buffer.Bytes(), nil
 }
 
-// writeTLV(buf, TagVersion, []byte{0x09})
-// writeTLV(buf, TagIntent, []byte{intentID})
+// writeTLV(buffer, TagVersion, []byte{0x09})
+// writeTLV(buffer, TagIntent, []byte{intentID})
 func writeTLV(writer io.Writer, tag uint8, value []byte) error {
 	// Check strict length constraint (1 byte length = max 255 bytes)
 	if len(value) > 255 {