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/lib.rs

@@ -77,5 +77,14 @@ pub use error::{ConfigError, DatasetError, SubcarrierError, TrainError};
 pub use error::TrainResult as TrainResultAlias;
 pub use subcarrier::{compute_interp_weights, interpolate_subcarriers, select_subcarriers_by_variance};
 
+// MERIDIAN (ADR-027) re-exports.
+pub use domain::{
+    AdversarialSchedule, DomainClassifier, DomainFactorizer, GradientReversalLayer,
+};
+pub use eval::CrossDomainEvaluator;
+pub use geometry::{FilmLayer, FourierPositionalEncoding, GeometryEncoder, MeridianGeometryConfig};
+pub use rapid_adapt::{AdaptError, AdaptationLoss, AdaptationResult, RapidAdaptation};
+pub use virtual_aug::VirtualDomainAugmentor;
+
 /// Crate version string.
 pub const VERSION: &str = env!("CARGO_PKG_VERSION");