Snapshot WIP: Probe calibration path, faer LU backend, and BPHX phase-change duty.

Checkpoint incomplete calibration work (cond SDT green, evap SST failing) plus related solver/UI changes so the next pass can fix and extend safely.

Co-authored-by: Cursor <cursoragent@cursor.com>

crates/solver/Cargo.toml

@@ -11,6 +11,7 @@ repository = "https://github.com/entropyk/entropyk"
 entropyk-components = { path = "../components" }
 entropyk-core = { path = "../core" }
 entropyk-solver-core = { path = "../solver-core" }
+faer = "0.24"
 nalgebra = "0.33"
 petgraph = "0.6"
 thiserror = "1.0"
@@ -29,6 +30,10 @@ criterion = "0.5"
 name = "lu_solve"
 harness = false
 
+[[bench]]
+name = "lu_backends"
+harness = false
+
 [[bench]]
 name = "residual_jacobian_assembly"
 harness = false