DADBEAR unit18: route staleness bridge to trace decide

[adamlevineagent]

Summary

• Route manual check-staleness calls through DADBEAR TRACE -> DECIDE compilation instead of the legacy staleness queue drain.
• Return supervisor DECIDE compilation metrics (decide_work, deltas_processed) from route/IPC responses.
• Add coverage proving the bridge compiles stale_check work items without writing pyramid_staleness_queue.

Verification

• cargo check --lib
• cargo test --lib trace_decide_check_compiles_work_without_legacy_queue -- --nocapture
• cargo test --lib test_empty_changed_files_returns_empty_report -- --nocapture
• cargo test --lib edge_survives_endpoint_supersession -- --nocapture
• cargo test --lib faq_link_survives_related_node_supersession -- --nocapture
• cargo test --lib targeted_evidence_resolves_real_source_not_placeholder -- --nocapture
• cargo test --lib stale_check_decision_ -- --nocapture
• cargo test --lib test_set_file_content_hash_preserves_node_ids_order_independent -- --nocapture
• cargo test --lib not_stale_pass_naturally_terminates_without_execute -- --nocapture
• cargo test --lib skip_abstain_naturally_terminates_without_execute -- --nocapture
• cargo test --lib phase0_stale_fail_safe_tests -- --nocapture
• git diff --check

Coordination

This unit does not touch Blue/co-owned write-path signatures (thread repoint, edge supersede, FAQ rewrite, annotation reparent). It only redirects the manual staleness bridge away from legacy queue writes into existing DADBEAR compiler/supervisor work-item flow.