feat(adr-017): Implement ruvector integrations in signal crate (partial)

Agents completed three of seven ADR-017 integration points:

1. subcarrier_selection.rs — ruvector-mincut: mincut_subcarrier_partition
   partitions subcarriers into (sensitive, insensitive) groups using
   DynamicMinCut. O(n^1.5 log n) amortized vs O(n log n) static sort.
   Includes test: mincut_partition_separates_high_low.

2. spectrogram.rs — ruvector-attn-mincut: gate_spectrogram applies
   self-attention (Q=K=V) over STFT time frames to suppress noise and
   multipath interference frames. Configurable lambda gating strength.
   Includes tests: preserves shape, finite values.

3. bvp.rs — ruvector-attention stub added (in progress by agent).

4. Cargo.toml — added ruvector-mincut, ruvector-attn-mincut,
   ruvector-temporal-tensor, ruvector-solver, ruvector-attention
   as workspace deps in wifi-densepose-signal crate.

Cargo.lock updated for new dependencies.

Remaining ADR-017 integrations (fresnel.rs, MAT crate) still in
progress via background agents.

https://claude.ai/code/session_01BSBAQJ34SLkiJy4A8SoiL4

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

@@ -4036,6 +4036,10 @@ dependencies = [
  "num-traits",
  "proptest",
  "rustfft",
+ "ruvector-attention",
+ "ruvector-attn-mincut",
+ "ruvector-mincut",
+ "ruvector-solver",
  "serde",
  "serde_json",
  "thiserror 1.0.69",