redfish: fix GPU duplication on Supermicro HGX, exclude NVSwitch, restore path dedup

Three bugs, all related to GPU dedup in the Redfish replay pipeline:

1. collectGPUsFromProcessors (redfish_replay.go): GPU-type Processor entries
   (Systems/HGX_Baseboard_0/Processors/GPU_SXM_N) were not deduplicated against
   existing PCIeDevice GPUs on Supermicro HGX. The chassis-ID lookup keyed on
   processor Id ("GPU_SXM_1") but the chassis is named "HGX_GPU_SXM_1" — lookup
   returned nothing, serial stayed empty, UUID was unseen → 8 duplicate GPU rows.
   Fix: read SerialNumber directly from the Processor doc first; chassis lookup
   is now a fallback override (as it was designed for MSI).

2. looksLikeGPU (redfish.go): NVSwitch PCIe devices (Model="NVSwitch",
   Manufacturer="NVIDIA") were classified as GPUs because "nvidia" matched the
   GPU hint list. Fix: early return false when Model contains "nvswitch".

3. gpuDocDedupKey (redfish.go): commit 9df29b1 changed the dedup key to prefer
   slot|model before path, which collapsed two distinct GPUs with identical model
   names in GraphicsControllers into one entry. Fix: only serial and BDF are used
   as cross-path stable dedup keys; fall back to Redfish path when neither is
   present. This also restores TestReplayCollectGPUs_DedupUsesRedfishPathBeforeHeuristics
   which had been broken on main since 9df29b1.

Added tests:
- TestCollectGPUsFromProcessors_SupermicroHGX: Processor GPU dedup when
  chassis-ID naming convention does not match processor Id
- TestReplayCollectGPUs_DedupCrossChassisSerial: same GPU via two Chassis
  PCIeDevice trees with matching serials → collapsed to one
- TestLooksLikeGPU_NVSwitchExcluded: NVSwitch is not a GPU

Added rule to bible-local/09-testing.md: dedup/filter/classify functions must
cover true-positive, true-negative, and the vendor counter-case axes.

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

internal/collector/redfish_replay.go

@@ -1476,11 +1476,16 @@ func (r redfishSnapshotReader) collectGPUsFromProcessors(systemPaths, chassisPat
 				continue
 			}
 
-			// Resolve serial from Chassis/<Id>.
+			// Resolve serial: prefer the processor doc itself (e.g. Supermicro
+			// HGX_Baseboard_0/Processors/GPU_SXM_N carries SerialNumber directly),
+			// then fall back to a matching chassis doc keyed by processor Id
+			// (e.g. MSI: Chassis/GPU_SXM_1/SerialNumber).
 			gpuID := strings.TrimSpace(asString(doc["Id"]))
-			serial := ""
+			serial := findFirstNormalizedStringByKeys(doc, "SerialNumber")
 			if chassisDoc, ok := chassisByID[strings.ToUpper(gpuID)]; ok {
-				serial = strings.TrimSpace(asString(chassisDoc["SerialNumber"]))
+				if cs := strings.TrimSpace(asString(chassisDoc["SerialNumber"])); cs != "" {
+					serial = cs
+				}
 			}
 
 			uuid := strings.TrimSpace(asString(doc["UUID"]))