Add DMI test fixtures from linuxhw/DMI and expand placeholder detection

Adds board and memory parser test fixtures based on real dmidecode output
from Dell PowerEdge R740xd, HPE ProLiant DL380 Gen10, and Supermicro
SYS-6028R-WTR sourced from the linuxhw/DMI dataset. Extends cleanDMIValue
with four additional vendor placeholder strings found in the dataset:
"0123456789", "1234567890", "NOT AVAILABLE", and "TO BE FILLED BY O.E.M"
(without trailing dot). Adds memory_test.go covering mixed populated/empty
DIMM slots and both GB and MB size formats.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

audit/internal/collector/board_test.go

@@ -84,6 +84,10 @@ func TestCleanDMIValue(t *testing.T) {
 		{"  Inspur  ", "Inspur"},
 		{"", ""},
 		{"0", ""},
+		{"0123456789", ""},
+		{"1234567890", ""},
+		{"Not Available", ""},
+		{"To Be Filled By O.E.M", ""},
 	}
 	for _, tt := range tests {
 		got := cleanDMIValue(tt.input)
@@ -109,6 +113,80 @@ func TestParseDMIFields(t *testing.T) {
 	}
 }
 
+func TestParseBoard_Dell(t *testing.T) {
+	type1 := mustReadFile(t, "testdata/dmidecode_type1_dell.txt")
+	type2 := mustReadFile(t, "testdata/dmidecode_type2_dell.txt")
+
+	board := parseBoard(type1, type2)
+
+	if board.SerialNumber != "7SG9F63" {
+		t.Errorf("serial_number: got %q, want %q", board.SerialNumber, "7SG9F63")
+	}
+	if board.Manufacturer == nil || *board.Manufacturer != "Dell Inc." {
+		t.Errorf("manufacturer: got %v, want Dell Inc.", board.Manufacturer)
+	}
+	if board.ProductName == nil || *board.ProductName != "PowerEdge R740xd" {
+		t.Errorf("product_name: got %v, want PowerEdge R740xd", board.ProductName)
+	}
+	// part number comes from type2 Product Name
+	if board.PartNumber == nil || *board.PartNumber != "0F9N89" {
+		t.Errorf("part_number: got %v, want 0F9N89", board.PartNumber)
+	}
+}
+
+func TestParseBoard_HPE(t *testing.T) {
+	type1 := mustReadFile(t, "testdata/dmidecode_type1_hpe.txt")
+	type2 := mustReadFile(t, "testdata/dmidecode_type2_hpe.txt")
+
+	board := parseBoard(type1, type2)
+
+	if board.SerialNumber != "CZJ9320CXN" {
+		t.Errorf("serial_number: got %q, want %q", board.SerialNumber, "CZJ9320CXN")
+	}
+	if board.Manufacturer == nil || *board.Manufacturer != "HPE" {
+		t.Errorf("manufacturer: got %v, want HPE", board.Manufacturer)
+	}
+	if board.ProductName == nil || *board.ProductName != "ProLiant DL380 Gen10" {
+		t.Errorf("product_name: got %v, want ProLiant DL380 Gen10", board.ProductName)
+	}
+	if board.PartNumber == nil || *board.PartNumber != "ProLiant DL380 Gen10" {
+		t.Errorf("part_number: got %v, want ProLiant DL380 Gen10", board.PartNumber)
+	}
+}
+
+func TestParseBoard_Supermicro_Placeholders(t *testing.T) {
+	type1 := mustReadFile(t, "testdata/dmidecode_type1_supermicro.txt")
+	type2 := mustReadFile(t, "testdata/dmidecode_type2_supermicro.txt")
+
+	board := parseBoard(type1, type2)
+
+	if board.SerialNumber != "S214726X2A36789" {
+		t.Errorf("serial_number: got %q, want %q", board.SerialNumber, "S214726X2A36789")
+	}
+	if board.Manufacturer == nil || *board.Manufacturer != "Supermicro" {
+		t.Errorf("manufacturer: got %v, want Supermicro", board.Manufacturer)
+	}
+	if board.ProductName == nil || *board.ProductName != "SYS-6028R-WTR" {
+		t.Errorf("product_name: got %v, want SYS-6028R-WTR", board.ProductName)
+	}
+	// "X10DRW-i" is the real part number from type 2
+	if board.PartNumber == nil || *board.PartNumber != "X10DRW-i" {
+		t.Errorf("part_number: got %v, want X10DRW-i", board.PartNumber)
+	}
+}
+
+func TestParseBIOSFirmware_Dell(t *testing.T) {
+	type0 := mustReadFile(t, "testdata/dmidecode_type0_dell.txt")
+	fw := parseBIOSFirmware(type0)
+
+	if len(fw) != 1 {
+		t.Fatalf("expected 1 firmware record, got %d", len(fw))
+	}
+	if fw[0].Version != "2.5.4" {
+		t.Errorf("version: got %q, want 2.5.4", fw[0].Version)
+	}
+}
+
 func mustReadFile(t *testing.T, path string) string {
 	t.Helper()
 	b, err := os.ReadFile(path)