DADBEAR unit20: delete staleness bridge

[adamlevineagent]

Summary

• Absorb the manual check-staleness request/response, observation-event auto-detect, and TRACE->DECIDE entrypoint into staleness.rs.
• Update route/IPC call sites to use pyramid::staleness directly.
• Remove staleness_bridge.rs and its module export.

Scope notes

• No Blue/co-owned cascade write helpers touched.
• This deletes the bridge file without dropping legacy DB queue tables yet; supersession.rs::record_supersession still has a live queue enqueue caller requiring a later unit/decision.

Verification

• cargo check --lib --message-format short
• cargo test --lib staleness::tests -- --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
• rg "staleness_bridge" src-tauri/src -n (no matches)
• git diff --check