feat: config-driven multi-scenario + gcda accumulation fix + gcov merge fix

Config-driven architecture:
- coverage_dates: YAML-driven date replacement for LEAVE_RECORDS
- row_overrides: per-scenario field overrides (e.g. STATUS='9')
- delete_all_rows: per-scenario table emptying for empty-cursor tests

gcda accumulation fix (V3 bug #7):
- Delete .gcda before each scenario run to prevent GnuCOBOL accumulation
- Force-copy scenario gcda (skip mtime check)
- Copy scenario DB to CWD data/kin.db for CONNECT TO path resolution

Multi-run gcov merge fix:
- Always merge multi-run gcov data regardless of generate_coverage flag
- Fix v3_root UnboundLocalError in cleanup path

Other fixes:
- _make_key_unique: skip WHERE-constrained columns to avoid PK conflict
- incremental_supplement: support fields_dict for base record generation
- check_coverage: use structure coverage data if available
- orchestrator.py: filter _-prefixed fields in TestCase; merge Agent2Data cases

cobol_testgen/coverage.py

@@ -1358,11 +1358,33 @@ def run_coverage(branch_tree, branch_paths_with_assigns, fields,
 def check_coverage(structure: dict, test_records: list[dict]) -> dict:
     total_paragraphs = structure.get("total_paragraphs", 0)
     total_branches = structure.get("total_branches", 0)
-    decision_points = structure.get("decision_points", [])
     has_data = len(test_records) > 0
 
     paragraph_rate = 1.0 if (total_paragraphs > 0 and has_data) else 0.0
 
+    cov = structure.get("coverage", {})
+    if cov and "total" in cov:
+        total = cov["total"]
+        covered = cov["covered"]
+        branch_rate = covered / max(total, 1) if total > 0 else 0.0
+        decision_rate = branch_rate
+
+        uncovered = []
+        for dp in cov.get("decision_points", []):
+            if dp["covered"] < dp["branches"]:
+                uncovered.append(dp["id"])
+
+        return {
+            "paragraph_rate": paragraph_rate,
+            "branch_rate": branch_rate,
+            "decision_rate": decision_rate,
+            "uncovered_decision_ids": uncovered,
+            "total_branches": total,
+            "total_paragraphs": total_paragraphs,
+            "records_count": len(test_records),
+            "note": "静态分析覆盖率（来自 mark_coverage）。精确数据通过 gcov 获取。",
+        }
+
     return {
         "paragraph_rate": paragraph_rate,
         "branch_rate": 0.0,