fix(workspace): unblock --no-default-features build on Windows (#366, #415)

[ruvnet]

Summary

Fixes #366 and the active half of #415: cargo build --workspace --no-default-features and cargo test --workspace --no-default-features now succeed on Windows without vcpkg/openblas.

Root cause

wifi-densepose-mat, wifi-densepose-sensing-server, and wifi-densepose-train all depended on wifi-densepose-signal with default features enabled, which means signal's default = [\"eigenvalue\"] pulled ndarray-linalg → openblas-src through the entire workspace. --no-default-features at the workspace root only applies to the target crate; transitive default features stay on. The CLAUDE.md-recommended Windows build path (cargo test --workspace --no-default-features) therefore could not actually opt out of BLAS.

Fix

Three one-liners on the signal dependency:

wifi-densepose-signal = { version = \"0.3.0\", path = \"../wifi-densepose-signal\", default-features = false }

…in mat/Cargo.toml, sensing-server/Cargo.toml, train/Cargo.toml. Plus one stale-test fix:

// signal/src/ruvsense/field_model.rs
#[cfg(feature = \"eigenvalue\")]
#[test]
fn test_estimate_occupancy_noise_only() { ... }

The test was already failing on main under --no-default-features (unwrapping the NotCalibrated stub returned when the BLAS-backed impl is compiled out) — this gate makes the workspace test claim hold true.

Validation

$ cargo check --workspace --no-default-features
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 5.87s

$ cargo test --workspace --no-default-features
… (lots of test results) …
Total: 1538 passed, 0 failed, 8 ignored

ESP32-S3 on COM7 was running unmodified firmware throughout and continued streaming live CSI (cb #15900, RSSI −44 dBm) before, during, and after these changes — server-side fix only, no firmware impact.

Notes on user reports

The E0432 unresolved import ruvector_mincut, E0425 CLASSES, and 5× E0499/E0502 borrow errors that the user reported in #366 against v0.6.2 source code are already fixed in different ways on main (ruvector-mincut is now declared, CLASSES was renamed to model.class_names, tracker_update uses the .take()+restore pattern). What was not fixed on main was the BLAS propagation — that's what this PR addresses.

Test plan

• cargo check --workspace --no-default-features succeeds on Windows
• cargo test --workspace --no-default-features → 1,538 passed, 0 failed
• ESP32-S3 on COM7 still streams CSI (unchanged firmware)
• CI: workspace tests on Linux + Windows runners
• CI: firmware build matrix unaffected (no firmware changes)

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