Add a typed-handle GraphBuilder authoring surface for blueprint topology:
node references become Copy NodeHandle values, ports/fields resolve by name
against the existing PortSpec.name/FieldSpec.name at a single fallible build()
terminal, lowering to the unchanged index-wired Composite (C23 holds by
construction — names never reach the compilat, mirroring param-name resolution).
Spec auto-signed under /boss: all objective gates green (precondition,
self-review, grounding-check PASS) and a unanimous five-lens spec-skeptic panel
(criterion, grounding, scope-fork, ambiguity, plan-readiness all SOUND).
The structural close of the SimBroker exposure/price swap (#21) is explicitly
out of scope, tracked as #65.
refs #64
