feat(ECR-007): Wyckoff Live Structure with Confirmed/Live isolation

Add live.py lifecycle and event candidates; assemble confirmed vs live
in engine; Summary partition; execution_signal source=confirmed only.
Keep strategies untouched; do not lower Confirmed thresholds for Live.

Co-authored-by: Cursor <cursoragent@cursor.com>

docs/HANDOFF/ECR-007-architect-to-engineer.md

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+# Handoff
+
+**From:** Architect  
+**To:** Engineer  
+**ECR:** ECR-007  
+**State:** build  
+**Date:** 2026-08-07  
+
+## Artifacts
+- [x] ECR-007 Approved
+- [x] BACKEND_DESIGN BD-2026-007
+- [x] Note WYCKOFF-LIVE-STRUCTURE-001 FROZEN
+- [ ] TEST_REPORT / CODE_REVIEW
+
+## Restrictions
+- Do not lower Confirmed thresholds
+- Do not let Live feed execution
+- Do not touch strategies/**
+
+## Goal
+Ship Confirmed/Live separation + tests + Summary; Gate PASS.