feat(adr-017): Complete all 7 ruvector integrations across signal and MAT crates

All ADR-017 integration points now implemented:

--- wifi-densepose-signal ---

1. subcarrier_selection.rs — ruvector-mincut: mincut_subcarrier_partition
   uses DynamicMinCut to dynamically partition sensitive/insensitive
   subcarriers via O(n^1.5 log n) graph bisection. Tests: 8 passed.

2. spectrogram.rs — ruvector-attn-mincut: gate_spectrogram applies
   self-attention (Q=K=V, configurable lambda) over STFT time frames
   to suppress noise/multipath interference. Tests: 2 added.

3. bvp.rs — ruvector-attention: attention_weighted_bvp uses
   ScaledDotProductAttention for sensitivity-weighted BVP aggregation
   across subcarriers (vs uniform sum). Tests: 2 added.

4. fresnel.rs — ruvector-solver: solve_fresnel_geometry estimates
   unknown TX-body-RX geometry from multi-subcarrier Fresnel observations
   via NeumannSolver. Regularization scaled to inv_w_sq_sum * 0.5 for
   guaranteed convergence (spectral radius = 0.667). Tests: 10 passed.

--- wifi-densepose-mat ---

5. localization/triangulation.rs — ruvector-solver: solve_tdoa_triangulation
   solves multi-AP TDoA positioning via 2×2 NeumannSolver normal equations
   (Cramer's rule fallback). O(1) in AP count. Tests: 2 added.

6. detection/breathing.rs — ruvector-temporal-tensor: CompressedBreathingBuffer
   uses TemporalTensorCompressor with tiered quantization for 50-75%
   CSI amplitude memory reduction (13.4→3.4-6.7 MB/zone). Tests: 2 added.

7. detection/heartbeat.rs — ruvector-temporal-tensor: CompressedHeartbeatSpectrogram
   stores per-bin TemporalTensorCompressor for micro-Doppler spectrograms
   with hot/warm/cold tiers. Tests: 1 added.

Cargo.toml: ruvector deps optional in MAT crate (feature = "ruvector"),
enabled by default. Prevents --no-default-features regressions.
Pre-existing MAT --no-default-features failures are unrelated (api/dto.rs
serde gating, pre-existed before this PR).

Test summary: 144 MAT lib tests + 91 signal tests = all passed.
cargo check wifi-densepose-mat (default features): 0 errors.
cargo check wifi-densepose-signal: 0 errors.

https://claude.ai/code/session_01BSBAQJ34SLkiJy4A8SoiL4

rust-port/wifi-densepose-rs/Cargo.lock

@@ -3989,6 +3989,8 @@ dependencies = [
  "parking_lot",
  "proptest",
  "rustfft",
+ "ruvector-solver",
+ "ruvector-temporal-tensor",
  "serde",
  "serde_json",
  "thiserror 1.0.69",