feat: add signed ROCm diagnostic lane

.scratch/distributed-gguf-runtime/evidence/DGR-001/quality-parity-diagnosis.md

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+# DGR-001 quality-parity evidence summary
+
+This summary is generated by `summarize-quality-parity.py` from signed reports.
+It contains no independent logit measurements or self-asserted verification flag.
+
+| Source | Device | Quality oracle | BF16 GGUF candidate | Exact | Similarity | Status |
+|---|---|---|---|---:|---:|---|
+| CPU v1 (`e4eedadf-22f6-4907-8990-985456961099`) | CPU | Transformers BF16 | llama.cpp BF16 | 0.3333 | 0.9471 | immutable `stop` |
+| ROCm diagnostic (`31bf44e7-ccd4-4277-84ac-c775dee65411`) | ROCm0 / Radeon 8060S | Transformers float32 | llama.cpp BF16 | 1.0000 | 1.0000 | diagnostic only |
+
+## Interpretation
+
+The CPU and ROCm rows use different plans, devices, kernels, and quality oracles.
+The CPU BF16 divergence remains unexplained and v1 remains `stop`. The signed
+ROCm report establishes the narrower fact that the same BF16 GGUF artifact
+matched the float32 oracle for all three GPU sequences with zero failures.
+Its signed backend detail records `ROCm0: Radeon 8060S Graphics` and measured
+`25/25` layer offload.
+
+No conversion corruption was observed in that three-sequence ROCm sample. This
+does not prove global conversion correctness and does not retroactively change
+or explain the CPU result. A future v2 should predeclare a float32 quality oracle
+separately from its BF16 performance reference and use a larger corpus.
+
+## Reproduction and bindings
+
+- CPU report SHA-256: `5d99a58806f39821c9206728047b8c5d605027d8a41b88639089b2418da890b5`
+- GPU report SHA-256: `527b33d03627d57d60b30331e6b9119f579a828d6f6acb5c74ca25bab0af5f3d`
+- BF16 GGUF SHA-256: `e842fdc35d7f00fda95a54e1b51731ba1d196aea45065cc9f46925fdc1d6f862`
+- Signer fingerprint: `8baca8742d9b3ed0c3fc54929c23f75ec8c1c739900aaf5334780d598ffa84de`
+- Exact verification command: see `commands.txt`.