Snapshot WIP: solver HP epic progress, BPHX/HX physics, BMAD skill refresh.

Capture uncommitted solver robustness work (regularization, domain errors, linear solver lifecycle, tube DP/MSH), web workbench updates, and synced BMAD skills across IDE agent folders before starting BPHX pressure-drop.

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

bindings/c/src/solver.rs

@@ -107,6 +107,7 @@ impl From<&EntropykPicardConfig> for entropyk_solver::PicardConfig {
 
 /// Configuration for the fallback solver (Newton → Picard).
 #[repr(C)]
+#[derive(Default)]
 pub struct EntropykFallbackConfig {
     /// Newton solver configuration.
     pub newton: EntropykNewtonConfig,
@@ -114,15 +115,6 @@ pub struct EntropykFallbackConfig {
     pub picard: EntropykPicardConfig,
 }
 
-impl Default for EntropykFallbackConfig {
-    fn default() -> Self {
-        Self {
-            newton: EntropykNewtonConfig::default(),
-            picard: EntropykPicardConfig::default(),
-        }
-    }
-}
-
 /// Opaque handle to a solver result.
 ///
 /// Create via `entropyk_solve_*()` functions.