Icons and library entries for new pathsim discrete and Polynomial blocks

[milanofthe]

Summary

Adds pathview support for the seven new pathsim blocks introduced in pathsim.blocks.discrete and pathsim.blocks.math:

• FirstOrderHold, DiscreteIntegrator, DiscreteDerivative, DiscreteStateSpace, DiscreteTransferFunction, TappedDelay, Polynomial

Changes

• NodeLibrary: renamed Mixed category to Discrete, kept its block shape (asymmetric corner radii). New blocks placed there; Polynomial placed in Algebraic.
• Icons (registry.ts, curves.ts):
  • FirstOrderHold — piecewise-linear plot through the same sample values as SampleHold, so the two icons read as a pair.
  • DiscreteIntegrator, DiscreteDerivative, DiscreteStateSpace, DiscreteTransferFunction — KaTeX math (transfer function or recurrence form).
  • Polynomial — KaTeX y = Σ c_k u^{n-k}.
  • TappedDelay — custom SVG with cross axes and four time-shifted pulse traces, matching the visual style of other plot icons.
• Port behaviour (uiConfig.ts): added Polynomial, FirstOrderHold, DiscreteIntegrator, DiscreteDerivative to syncPortBlocks (1 input default, outputs mirror inputs for parallel vectorisation). DiscreteStateSpace left free (true MIMO, like StateSpace).
• Generated registry (generated/blocks.ts): re-extracted from local pathsim (75 → 82 blocks). TappedDelay now ships with inputs: ["in"] thanks to the matching pathsim PR adding input_port_labels.