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/to_sql.py

@@ -434,12 +434,14 @@ def build_db_input(
                 if sc not in [c['name'] for c in col_infos]:
                     col_infos.append({'name': sc, 'db_type': 'CHAR', 'size': 20})
 
+            where_cols = set()
             for col_info in col_infos:
                 col_name = col_info['name']
                 val = None
                 for wc in where_cons:
                     if wc['type'] == 'literal' and wc.get('col', '').upper() == col_name:
                         val = wc.get('literal', '')
+                        where_cols.add(col_name)
                         break
                     if wc['type'] == 'host_var':
                         hv = wc.get('host_var', '').upper()
@@ -473,7 +475,7 @@ def build_db_input(
 
             if col_infos:
                 first_col = col_infos[0]['name']
-                if first_col in row:
+                if first_col in row and (not where_cols or first_col not in where_cols):
                     row[first_col] = _make_key_unique(row[first_col], path_idx, seen_keys[table])
 
             db_input[table].append(row)