fix: harden MERIDIAN modules from code review + security audit

- domain.rs: atomic instance counter for unique Linear weight seeds (C3)
- rapid_adapt.rs: adapt() returns Result instead of panicking (C5),
  bounded calibration buffer with max_buffer_frames cap (F1-HIGH),
  validate lora_rank >= 1 (F10)
- geometry.rs: 24-bit PRNG precision matching f32 mantissa (C2)
- virtual_aug.rs: guard against room_scale=0 division-by-zero (F6)
- signal/lib.rs: re-export AmplitudeStats from hardware_norm (W1)
- train/lib.rs: crate-root re-exports for all MERIDIAN types (W2)

All 201 tests pass (96 unit + 24 integration + 18 subcarrier +
10 metrics + 7 doctests + 105 signal + 10 validation + 1 signal doctest).

Co-Authored-By: claude-flow <ruv@ruv.net>

rust-port/wifi-densepose-rs/crates/wifi-densepose-train/src/virtual_aug.rs

@@ -149,8 +149,8 @@ impl VirtualDomainAugmentor {
         let mut out = Vec::with_capacity(n);
         for (k, &val) in frame.iter().enumerate() {
             let k_f = k as f32;
-            // 1. Room-scale amplitude attenuation
-            let scaled = val / domain.room_scale;
+            // 1. Room-scale amplitude attenuation (guard against zero scale)
+            let scaled = if domain.room_scale.abs() < 1e-10 { val } else { val / domain.room_scale };
             // 2. Reflection coefficient modulation (per-subcarrier)
             let refl = domain.reflection_coeff
                 + (1.0 - domain.reflection_coeff) * (PI * k_f / n_f).cos();