feat(orchestration): compile agency strategies to CompiledExecutionGraph for real DAG execution

Add graphCompiler.ts that transforms each agency() strategy (sequential,
parallel, debate, review-loop, hierarchical) into a CompiledExecutionGraph
suitable for execution by GraphRuntime. This bridges the high-level agency
API to the full orchestration engine, enabling checkpointing, structured
state passing, conditional edge routing, and serializable IR for agency
runs.

Each strategy maps to a distinct graph topology:
- sequential: linear A -> B -> C chain
- parallel: fan-out/fan-in with synthesizer node
- debate: round-based sequential chain with concat reducer
- review-loop: producer -> reviewer -> conditional back-edge
- hierarchical: single manager GMI node with delegation tools

Includes mapGraphResultToAgencyResult and mapGraphEventToAgencyEvent
for translating between graph-level and agency-level event vocabularies.

Author: jddunn