feat(audit): 1.2 — board collector (dmidecode types 0, 1, 2)

- board.go: collectBoard(), parseBoard(), parseBIOSFirmware(), parseDMIFields(), cleanDMIValue()
- Reads System Information (type 1): serial, manufacturer, product_name, uuid
- Reads Base Board Information (type 2): part_number
- Reads BIOS Information (type 0): firmware version record
- cleanDMIValue strips vendor placeholders (O.E.M., Not Specified, Unknown, etc.)
- board_test.go: 6 table/case tests with dmidecode fixtures in testdata/
- collector.go: wired board + BIOS firmware into snapshot

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

audit/internal/collector/testdata/dmidecode_type0.txt

@@ -0,0 +1,25 @@
+# dmidecode 3.5
+Getting SMBIOS data from sysfs.
+SMBIOS 3.1.1 present.
+
+Handle 0x0000, DMI type 0, 26 bytes
+BIOS Information
+	Vendor: American Megatrends Inc.
+	Version: 06.08.05
+	Release Date: 12/20/2023
+	Address: 0xF0000
+	Runtime Size: 64 kB
+	ROM Size: 32 MB
+	Characteristics:
+		PCI is supported
+		PCI Express is supported
+		BIOS is upgradeable
+		BIOS shadowing is allowed
+		Selectable boot is supported
+		ACPI is supported
+		USB legacy is supported
+		BIOS boot specification is supported
+		Targeted content distribution is supported
+		UEFI is supported
+	BIOS Revision: 5.22
+	Firmware Revision: 4.1

audit/internal/collector/testdata/dmidecode_type1.txt

@@ -0,0 +1,14 @@
+# dmidecode 3.5
+Getting SMBIOS data from sysfs.
+SMBIOS 3.1.1 present.
+
+Handle 0x0001, DMI type 1, 27 bytes
+System Information
+	Manufacturer: Inspur
+	Product Name: NF5468M7
+	Version: To Be Filled By O.E.M.
+	Serial Number: CAR315KA0803B90
+	UUID: a1b2c3d4-e5f6-7890-abcd-ef1234567890
+	Wake-up Type: Power Switch
+	SKU Number: To Be Filled By O.E.M.
+	Family: To Be Filled By O.E.M.

audit/internal/collector/testdata/dmidecode_type1_empty_serial.txt

@@ -0,0 +1,14 @@
+# dmidecode 3.5
+Getting SMBIOS data from sysfs.
+SMBIOS 3.1.1 present.
+
+Handle 0x0001, DMI type 1, 27 bytes
+System Information
+	Manufacturer: To Be Filled By O.E.M.
+	Product Name: To Be Filled By O.E.M.
+	Version: To Be Filled By O.E.M.
+	Serial Number: To Be Filled By O.E.M.
+	UUID: Not Settable
+	Wake-up Type: Power Switch
+	SKU Number: To Be Filled By O.E.M.
+	Family: To Be Filled By O.E.M.

audit/internal/collector/testdata/dmidecode_type2.txt

@@ -0,0 +1,15 @@
+# dmidecode 3.5
+Getting SMBIOS data from sysfs.
+SMBIOS 3.1.1 present.
+
+Handle 0x0002, DMI type 2, 15 bytes
+Base Board Information
+	Manufacturer: Inspur
+	Product Name: YZCA-02758-105
+	Version: To Be Filled By O.E.M.
+	Serial Number: CAR315KA0803B90
+	Asset Tag: To Be Filled By O.E.M.
+	Features:
+		Board is a hosting board
+	Location In Chassis: To Be Filled By O.E.M.
+	Type: Motherboard