feat: Implement ADR-014 SOTA signal processing (6 algorithms, 83 tests)

Add six research-grade signal processing algorithms to wifi-densepose-signal:

- Conjugate Multiplication: CFO/SFO cancellation via antenna ratio (SpotFi)
- Hampel Filter: Robust median/MAD outlier detection (50% contamination resistant)
- Fresnel Zone Model: Physics-based breathing detection from chest displacement
- CSI Spectrogram: STFT time-frequency generation with 4 window functions
- Subcarrier Selection: Variance-ratio ranking for top-K motion-sensitive subcarriers
- Body Velocity Profile: Domain-independent Doppler velocity mapping (Widar 3.0)

All 313 workspace tests pass, 0 failures. Updated README with new capabilities.

https://claude.ai/code/session_01Ki7pvEZtJDvqJkmyn6B714

rust-port/wifi-densepose-rs/crates/wifi-densepose-signal/src/lib.rs

@@ -31,10 +31,16 @@
 //! let processor = CsiProcessor::new(config);
 //! ```
 
+pub mod bvp;
 pub mod csi_processor;
+pub mod csi_ratio;
 pub mod features;
+pub mod fresnel;
+pub mod hampel;
 pub mod motion;
 pub mod phase_sanitizer;
+pub mod spectrogram;
+pub mod subcarrier_selection;
 
 // Re-export main types for convenience
 pub use csi_processor::{