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

config/programs/KIN03EXP.yaml

@@ -35,3 +35,47 @@ subprograms:
   - SUB01DAT
   - SUB02MSG
   - SUB03END
+
+coverage_dates:
+  LEAVE_RECORDS:
+    - start: "20260701"
+      end: "20260701"
+      emp: "00000001"
+    - start: "20260702"
+      end: "20260702"
+      emp: "00000001"
+    - start: "20260704"
+      end: "20260704"
+      emp: "00000001"
+    - start: "20260705"
+      end: "20260705"
+      emp: "00000001"
+    - start: "20260131"
+      end: "20260203"
+      emp: "00000002"
+    - start: "20260430"
+      end: "20260502"
+      emp: "00000002"
+    - start: "20240228"
+      end: "20240302"
+      emp: "00000003"
+    - start: "20230228"
+      end: "20230302"
+      emp: "00000003"
+    - start: "20240229"
+      end: "20240302"
+      emp: "00000004"
+    - start: "20230227"
+      end: "20230302"
+      emp: "00000004"
+    - start: "20261230"
+      end: "20270101"
+      emp: "00000099"
+
+runs:
+  - id: normal
+  - id: empty_cursor
+    delete_all_rows: true
+    row_overrides:
+      LEAVE_RECORDS:
+        STATUS: "9"