refactor: dedupe status-severity ranking and small webui helpers

statusSeverity was byte-for-byte duplicated in collector/contract.go and
app/sat_overlay.go (same switch, same comment). Export it as
collector.StatusSeverity and drop the app-package copy.

page_topo.go inlined the same GPU/NIC/RAID class switch as its own
pcieDeviceKind function in one spot — call the function instead.

page_validate.go had its own copy of pages.go's firstNonEmpty (all call
sites already pre-trim their inputs via validateTrimPtr, so the extra
TrimSpace was redundant) — drop the duplicate.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

audit/internal/webui/page_topo.go

@@ -614,15 +614,8 @@ func renderTopoMainDiagram(hw schema.HardwareSnapshot, exportDir string) string
 	}
 	var placed []placedDevice
 	for _, dev := range hw.PCIeDevices {
-		var kind string
-		switch {
-		case dev.DeviceClass != nil && isGPUDeviceClass(*dev.DeviceClass):
-			kind = "gpu"
-		case isNICDeviceClassDev(dev):
-			kind = "nic"
-		case dev.DeviceClass != nil && isRAIDControllerClass(*dev.DeviceClass):
-			kind = "raid"
-		default:
+		kind := pcieDeviceKind(dev)
+		if kind == "" {
 			continue
 		}
 		col := unknownCol