Feature/process wait

[Lorchie]

Summary

Adds two independent workflow features:

• Wait node — a built-in node that pauses workflow execution at any point in the chain, with a Continue button to resume. Visible in
  the Generate panel when pinned via the eye toggle.
• Conditional params (show_if) — extension param schemas can now declare a show_if clause to hide irrelevant params based on
  other params' values.

Wait node

• New built-in node waitNode, neutral grey passthrough (any type).
• When the runner reaches a Wait node, runState.status becomes paused and a Continue button shows in the node's subheader.
• Clicking Continue resumes execution at the next node; Cancel also unblocks the pause.
• Eye toggle (showInGenerate) makes the node available in the Generate panel as a WaitParamRow with the same Continue button.

Two related runner improvements were needed for this to work well with Add to Scene:

• currentJob is updated as soon as a node feeds an outputNode, so the 3D viewer loads progressively instead of waiting for the full
  run (useful when Wait pauses for a long time).
• When multiple Add to Scene nodes exist, the last one in topo order determines the final scene mesh.

Conditional params (show_if)

• ParamSchema gains an optional show_if?: Record<string, value | value[]>.
• ExtensionNode filters params by visibility before rendering: a param is shown only if every show_if entry matches the current value
  (or default) of the referenced param.
• Supports equality (mode: "advanced") and inclusion (mode: ["fast", "medium"]).