feat(adr-185): P4 benchmarks, examples, and README extras for the SOTA wheels

ADR-185 §4.2 pytest-benchmark micro-benchmarks + runnable examples +
README extras table for the aether/meridian/mat bindings.

- python/bench/test_bench_{aether,meridian,mat}.py — follow the existing
  test_bench_vitals.py pattern (skipped by default; --benchmark-only).
- python/examples/{reid_from_csi,cross_room_calibrate,mat_triage}.py —
  typed, runnable, mypy --strict clean.
- python/README.md — SOTA extras table + example links.

Measured on a RELEASE wheel (maturin develop --release --features sota),
reference machine per ADR-117 §10:
  AETHER embed()          mean ~150 us/window   (target <2 ms)   PASS
    batch scaling 1/8/64: 140 / 1091 / 8509 us  (linear, no O(n^2)) PASS
  MERIDIAN normalize()    mean ~2.2 us/frame     (target <200 us) PASS
  MERIDIAN encode()       mean ~6.9 us           (target <200 us) PASS
  MAT ingest+scan_once()  mean ~40 ms/256-frame  (< 500 ms interval) PASS

Acceptance self-verification (ADR-185 §6), all run just now:
  §6.1 default wheel 279 KB (<=5 MB); build_features has no p6-* feature  PASS
  §6.2 pytest tests/test_aether.py    9/9   PASS
  §6.3 pytest tests/test_meridian.py  13/13 PASS
  §6.4 pytest tests/test_mat.py       7/7   PASS
  §6.5 benchmarks meet all targets (above)                                PASS
  §6.6 parity harness: 3/3 SHA golden gates green (cargo test --features
       sota, 6/6); CI *wiring* as a release gate is out of python/ scope  PARTIAL
  §6.7 SOTA accuracy bars on labeled fixtures: NOT met (no labeled
       fixtures / trained models available; parity proves path-equality,
       not accuracy)                                                       OPEN
  §6.8 .pyi stubs present for all three; mypy --strict on the 3 examples   PASS
  §6.9 base wheel `import wifi_densepose.{aether,meridian,mat}` raises a
       clear ImportError naming the extra                                  PASS
  No regression: 76 pre-existing tests pass on the default wheel.

Status NOT flipped to Accepted: §6.7 (accuracy bars) is unmet, §6.6 CI
wiring is pending, and the per-extra wheel-size hoists (sensing-server /
train / mat leaf crates) remain follow-ups. docs/adr/ is owned by another
agent this session, so the ADR ledger edit is deferred to that owner.

python/bench/test_bench_aether.py

@@ -0,0 +1,44 @@
+"""ADR-185 §4.2 — AETHER embed() micro-benchmarks.
+
+Target (release build, ADR-024 §2.8 FP32 <1 ms with headroom): steady-state
+`embed()` < 2 ms/window, and batched `embed()` scales roughly linearly (no
+accidental O(n²)).
+
+Run with:
+    pytest python/bench/test_bench_aether.py --benchmark-only
+
+Skipped by default (they live in `bench/`, outside `testpaths`). Timing
+targets are validated on a RELEASE wheel (`maturin develop --release
+--features sota`); a debug wheel will be several× slower.
+"""
+
+from __future__ import annotations
+
+import math
+
+import pytest
+
+from wifi_densepose import aether
+
+
+def _window(frames: int = 8, subc: int = 56) -> list[list[float]]:
+    return [[math.sin(0.1 * t + 0.03 * k) for k in range(subc)] for t in range(frames)]
+
+
+def _extractor() -> aether.EmbeddingExtractor:
+    return aether.EmbeddingExtractor(n_subcarriers=56, config=aether.AetherConfig())
+
+
+def test_embed_per_window(benchmark) -> None:
+    ext = _extractor()
+    window = _window()
+    out = benchmark(lambda: ext.embed(window))
+    assert len(out) == 128
+
+
+@pytest.mark.parametrize("batch", [1, 8, 64])
+def test_embed_batch_scaling(benchmark, batch: int) -> None:
+    ext = _extractor()
+    windows = [_window() for _ in range(batch)]
+    out = benchmark(lambda: [ext.embed(w) for w in windows])
+    assert len(out) == batch