fp-hw-survey capture: Snapdragon X-series (arm64/Windows-on-ARM)

Capture native FP behavior on a **Snapdragon X-series** part (e.g. X Elite, `aarch64` / Windows-on-ARM) with `crates/fp-hw-survey`.

### Steps
```powershell
cargo build --release -p fp-hw-survey
.\target\release\fp-hw-survey.exe info # confirm CPU brand + features
.\target\release\fp-hw-survey.exe selftest # must pass
.\target\release\fp-hw-survey.exe capture --label snapdragon-x-elite-win
```

### What to attach to this issue
- The `info` output (CPU brand + detected features).
- The `selftest` result (must be clean — `capture` refuses to write otherwise).
- The **one-line NDJSON header** from the capture (durable provenance: cpu / os / features / date).
- The `capture-*.ndjson` file itself (attachment or link).

### Notes
- On Windows-on-ARM there is no CPUID; brand comes from the registry `ProcessorNameString`, and `fp16` from `IsProcessorFeaturePresent`. **`rpres`/`afp` are best-effort here** — Windows exposes no `PF_*` flag for them, so they may be absent from `features` even if the silicon supports them; note this when interpreting any single-precision estimate divergence.

Part of the FP hardware survey fleet-capture campaign.