feat(adr-117/p3+p3.5): vitals + BFLD bindings

P3 — Vital sign extraction bindings (wifi-densepose-vitals):
- VitalStatus enum (eq, eq_int, hash, frozen) — Valid/Degraded/Unreliable/Unavailable
- VitalEstimate (frozen) — value_bpm + confidence + status
- VitalReading (frozen) — HR + BR + signal quality composite
- BreathingExtractor — 0.1–0.5 Hz bandpass + zero-crossing
- HeartRateExtractor — 0.8–2.0 Hz bandpass + autocorrelation
- py.allow_threads on extract() hot loops (Q5 audit confirmed
  core/vitals/signal are pure-sync — zero tokio deps, safe to release
  GIL with no embedded runtime needed)
- 17 tests covering construction, getters, frozen immutability,
  esp32_default + explicit ctors, synthetic-signal end-to-end

P3.5 — BFLD bindings (forward-compat surface, stub Rust):
- BfldKind enum — CompressedHE20/40/80/160 + UncompressedHT20/40
  with n_subcarriers, bandwidth_mhz, is_he metadata getters
- BfldFrame (frozen) — from_compressed_feedback() accepts numpy
  Complex64 ndarray [Nr x Nc x Nsc], validates dims against kind,
  feedback_matrix() returns lossless roundtrip ndarray
- BfldReport — aggregates frames, rejects mismatched kinds,
  computes inverse-CV coherence score
- 19 tests covering all 6 PHY variants + numpy roundtrip +
  dim-mismatch error + aggregation
- Real Rust ingestion (wifi-densepose-bfld crate) lands post-v2.0
  per ADR-117 §11.11/12 — Python API will not change

Total Python test count: 93 (was 57, +36 P3+P3.5). All passing.

Refs: docs/adr/ADR-117-pip-wifi-densepose-modernization.md
Refs: #785

Co-Authored-By: claude-flow <ruv@ruv.net>

python/wifi_densepose/__init__.py

@@ -45,6 +45,18 @@ BoundingBox = _native.BoundingBox
 PersonPose = _native.PersonPose
 PoseEstimate = _native.PoseEstimate
 
+# ─── P3 — Vital sign extraction ──────────────────────────────────────
+VitalStatus = _native.VitalStatus
+VitalEstimate = _native.VitalEstimate
+VitalReading = _native.VitalReading
+BreathingExtractor = _native.BreathingExtractor
+HeartRateExtractor = _native.HeartRateExtractor
+
+# ─── P3.5 — BFLD (Beamforming Feedback Loop Data) ─────────────────────
+BfldKind = _native.BfldKind
+BfldFrame = _native.BfldFrame
+BfldReport = _native.BfldReport
+
 
 __rust_version__: str = _native.__rust_version__
 """Version of the bound Rust core. Useful for bug reports."""
@@ -80,4 +92,14 @@ __all__ = [
     "BoundingBox",
     "PersonPose",
     "PoseEstimate",
+    # P3 — vital sign extraction
+    "VitalStatus",
+    "VitalEstimate",
+    "VitalReading",
+    "BreathingExtractor",
+    "HeartRateExtractor",
+    # P3.5 — BFLD (forward-compat surface for the future Rust crate)
+    "BfldKind",
+    "BfldFrame",
+    "BfldReport",
 ]