Add deterministic, durable SCUD v2 harness

[pyrex41]

What changed

• adds the deterministic v2 goal/reducer/reconciler and DAG bridge
• makes budget exhaustion and runner progress durable and terminal
• adds td-backed fenced event persistence and authorization
• canonicalizes complete rho.run/v1 requests before BIP340 signing
• expands CI coverage to the v2 command and agent branches

Architecture

SCUD is the small embeddable Go goal/DAG harness. td keeps its semantic core in Shen, with Lua/OpenResty for HTTP, storage, and crypto seams. A Go td worker can embed this package and replace td’s legacy Python supervisor. Rho owns bounded provider/tool execution across Anthropic, OpenAI, and xAI.

Validation

• go test ./...