Add diagram workbench UI with Modelica DoF coaching and ISO glyphs.

Ship the Next.js cycle editor with CAD chrome, technical HX symbols, Fixed/Free boundary guidance, and secondary water/air pressure drop support in the solver stack.

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

apps/web/public/docs/components/flow-regularization.md

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+# Flow regularization (zero-flow helpers)
+
+Source: `crates/components/src/heat_exchanger/flow_regularization.rs`  
+Used by: **FloodedEvaporator** (full residual path); **Condenser** / **Evaporator** (smooth `|ṁ|` for live `C_sec`).
+
+---
+
+## EN
+
+### Why
+
+Zero mass flow is a **valid** state (staging, circuit off, Newton trial steps). Hard branches like `if |m| < ε { Q = 0 }` create **Jacobian discontinuities**.
+
+### API
+
+| Function | Meaning |
+|----------|---------|
+| `flow_activity(m, ε)` | α = m²/(m²+ε²) ∈ [0,1), α(0)=0 |
+| `flow_activity_derivative` | dα/dm |
+| `effective_duty(Q, α_a, α_b)` | Q_eff = α_a · α_b · Q |
+| `blend_transport_residual` | blend active transport residual with Δh hold |
+| `blend_transport_partials` | analytic partials of the blend |
+| `smooth_mass_magnitude` | C¹-ish smooth \|m\| for `C = \|ṁ\| · cp` |
+| `smooth_mass_magnitude_derivative` | d\|m\|_smooth / dm |
+
+Defaults: `DEFAULT_M_EPS_KG_S = 1e-4`, `DEFAULT_M_SCALE_KG_S = 0.05`.
+
+### Interaction with rating mode (Flooded)
+
+On **FloodedEvaporator system path** (live secondary): duty uses `effective_duty` with α_ref and α_sec.  
+On **Flooded rating path** (scalar C_sec only): residual energy uses **full Q** (no α_ref gate) so `ṁ_ref = 0` is not a trivial root when `C_sec > 0`.
+
+### DoF rule
+
+Regularization **must not** change `n_equations()`. It only reshapes residual values and derivatives.
+
+---
+
+## FR
+
+### Pourquoi
+
+Le débit nul est un état **valide**. Les `if |m| < ε` durs cassent le Newton.
+
+### API
+
+Voir le tableau EN.
+
+### Rating vs système (Flooded)
+
+- **Système (ports live)** : duty régularisée α_ref · α_sec · Q.  
+- **Rating (scalaires)** : Q **plein** dans le résidu énergie (pas de racine triviale ṁ=0).
+
+### Règle DoF
+
+La régularisation **ne change pas** `n_equations()`.