feat: Complete Rust port of WiFi-DensePose with modular crates

Major changes:
- Organized Python v1 implementation into v1/ subdirectory
- Created Rust workspace with 9 modular crates:
  - wifi-densepose-core: Core types, traits, errors
  - wifi-densepose-signal: CSI processing, phase sanitization, FFT
  - wifi-densepose-nn: Neural network inference (ONNX/Candle/tch)
  - wifi-densepose-api: Axum-based REST/WebSocket API
  - wifi-densepose-db: SQLx database layer
  - wifi-densepose-config: Configuration management
  - wifi-densepose-hardware: Hardware abstraction
  - wifi-densepose-wasm: WebAssembly bindings
  - wifi-densepose-cli: Command-line interface

Documentation:
- ADR-001: Workspace structure
- ADR-002: Signal processing library selection
- ADR-003: Neural network inference strategy
- DDD domain model with bounded contexts

Testing:
- 69 tests passing across all crates
- Signal processing: 45 tests
- Neural networks: 21 tests
- Core: 3 doc tests

Performance targets:
- 10x faster CSI processing (~0.5ms vs ~5ms)
- 5x lower memory usage (~100MB vs ~500MB)
- WASM support for browser deployment

rust-port/wifi-densepose-rs/crates/wifi-densepose-signal/Cargo.toml

@@ -0,0 +1,26 @@
+[package]
+name = "wifi-densepose-signal"
+version.workspace = true
+edition.workspace = true
+description = "WiFi CSI signal processing for DensePose estimation"
+license.workspace = true
+
+[dependencies]
+# Core utilities
+thiserror.workspace = true
+serde = { workspace = true }
+serde_json.workspace = true
+chrono = { version = "0.4", features = ["serde"] }
+
+# Signal processing
+ndarray = { workspace = true }
+rustfft.workspace = true
+num-complex.workspace = true
+num-traits.workspace = true
+
+# Internal
+wifi-densepose-core = { path = "../wifi-densepose-core" }
+
+[dev-dependencies]
+criterion.workspace = true
+proptest.workspace = true