fp-hw-survey capture: Apple Silicon (M-series, arm64/macOS)

Capture native FP behavior on **Apple Silicon** (M1/M2/M3/M4, `aarch64` / macOS) with `crates/fp-hw-survey`.

### Steps
```sh
cargo build --release -p fp-hw-survey
./target/release/fp-hw-survey info # confirm CPU brand + features (expect fp16; rpres/afp if present)
./target/release/fp-hw-survey selftest # must pass
./target/release/fp-hw-survey capture --label m-mac
```

### 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
- `fp16` is expected on all shipping M-series; `rpres`/`afp` recorded if detected.
- Intra-ARMv8 estimate ops (`frecpe`/`frsqrte`/`frecpx`/`fmulx`) are predicted to be bit-identical with other ARMv8 parts — a zero-divergence merge against them is the expected, informative result.

Part of the FP hardware survey fleet-capture campaign.