XY-853: Implement internal Execution Program DAG readiness model

[yvette-carlisle]

Summary

• Add internal decodex.execution_program/1 model with node stages, dependencies, conflict domains, queue intent, drift detection, readiness reasons, and Linear issue mapping.
• Persist Execution Programs in runtime SQLite and expose compact operator status summaries without graph operations as the primary UX.
• Update loop runtime, runtime, tracker-tools, ledger, and operator-control-plane docs for the internal model boundary.

Validation

• cargo make fmt
• cargo make lint-fix
• cargo make test (996 passed, 1 skipped)
• semantic drift helper: pass, no stale phrase hits or removed terms