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/examples/reid_from_csi.py

@@ -0,0 +1,39 @@
+"""AETHER re-identification from CSI (ADR-185 P1, `[aether]` extra).
+
+Compute 128-dim contrastive embeddings for CSI windows and score them by
+cosine similarity — the primitive behind room fingerprinting and person
+re-identification.
+
+    pip install wifi-densepose[aether]
+    python examples/reid_from_csi.py
+"""
+
+from __future__ import annotations
+
+import math
+
+from wifi_densepose.aether import AetherConfig, EmbeddingExtractor, cosine_similarity
+
+
+def make_window(phase_shift: float, frames: int = 8, subc: int = 56) -> list[list[float]]:
+    """A synthetic CSI window; `phase_shift` stands in for a different scene."""
+    return [
+        [math.sin(0.1 * t + 0.03 * k + phase_shift) for k in range(subc)]
+        for t in range(frames)
+    ]
+
+
+def main() -> None:
+    ext = EmbeddingExtractor(n_subcarriers=56, config=AetherConfig())
+
+    same_a = ext.embed(make_window(0.0))
+    same_b = ext.embed(make_window(0.0))  # same scene
+    other = ext.embed(make_window(1.5))   # different scene
+
+    print(f"embedding dim:        {len(same_a)}")
+    print(f"same-scene similarity:  {cosine_similarity(same_a, same_b):.4f}")
+    print(f"cross-scene similarity: {cosine_similarity(same_a, other):.4f}")
+
+
+if __name__ == "__main__":
+    main()