Complete Studio Script member lifecycle gating and invoke contract handling

[potter-sun]

Problem

Studio can edit and draft-run Script implementations, but the member lifecycle still behaves as workflow-first. Script cannot reliably move through save observation, bind, invoke, and observe as a first-class member without risking stale source or incorrect endpoint assumptions.

Scope

• Add Script Build state handoff from StudioScriptBuildPanel to the Studio parent.
• Only expose a Script pending bind candidate after the saved revision is observed as applied in the script catalog.
• Add a Script branch in the parent bind handler that calls studioApi.bindScopeScript.
• Refetch/select the bound service after binding.
• Make Invoke use the bound service endpoint contract instead of assuming every Script supports chat stream.
• Keep draft-run inside Build and do not treat draft-run as proof that the member is bound or invokable.

Acceptance Criteria

• Dirty Script source does not create a bind candidate.
• Save accepted but not catalog-applied Script source does not create a bind candidate.
• Catalog-applied Script revision creates a Script pending bind candidate.
• Binding that candidate calls studioApi.bindScopeScript, not bindScopeWorkflow.
• Invoke defaults to chat only when the bound Script service exposes a chat-compatible endpoint.
• Non-chat Script endpoints show an honest contract/blocked state instead of pretending chat works.
• Frontend tests cover save-observed gating, Script bind, and non-chat invoke behavior.