feat: 리밸런싱 엔진 V1 + GAS 버그 수정 (2026-06-13)

주요 변경:
- tools/build_rebalance_engine_v1.py: REBALANCE_ENGINE_V1 신규
  * account_snapshot 직접 합산(_build_snap_position_map) → 소수주 분리 행 병합
  * 레짐 소스 macro.REGIME_PRELIM 최우선 (GAS 와 동일)
- src/gas_adapter_parts/gdf_06_rebalance.gs: runRebalanceSheet_() 신규
  * Logger.log / getSpreadsheet_() 로 run_all 연동 수정
- src/gas_adapter_parts/gdc_01_fetch_fundamentals.gs
  * _mergePositionRecord_(): 소수주 중복 행 합산 신규
  * parseInt → parseFloat (qty, availQty)
- src/gas_adapter_parts/gdf_01_price_metrics.gs
  * 미보유 종목 SELL_READY → WATCH_EXIT_SIGNAL
- spec/41_release_dag.yaml: build_rebalance_sheet 노드 추가 (step_count 63)
- spec/51_formula_lifecycle_registry.yaml: REBALANCE_ENGINE_V1 등록

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

examples/buy_case.yaml

@@ -0,0 +1,18 @@
+case_id: EX_BUY_001
+type: BUY
+input_summary:
+  data_status: "all_required_fields_ok"
+  hard_filters: "pass"
+  flow_rows: 20
+  atr20_status: "OK"
+  total_heat_pct: 5.5
+  expected_edge: 2.1
+expected_output:
+  investment_action: "BUY"
+  grade: "A"
+  required_order_fields: ["account", "ticker", "limit_price", "quantity", "stop_price", "stop_quantity", "take_profit_price", "take_profit_quantity"]
+  rule_ids_used:
+    - "risk_policy.master_prohibitions"
+    - "data_contract.data_completeness_gate"
+    - "position_sizing.volatility_targeting"
+    - "output_schema.buy_proposal_template.validation"