Add report deduplication and single-report deletion

Agent-Logs-Url: https://github.com/christianlouis/dmarq/sessions/37d68c2c-7cc8-45e4-bac3-e2e6f1611c6a

Co-authored-by: christianlouis <361235+christianlouis@users.noreply.github.com>

backend/app/tests/test_report_store.py

@@ -77,3 +77,67 @@ class TestReportStore:
     def test_delete_nonexistent_domain(self):
         store = ReportStore.get_instance()
         assert store.delete_domain_with_cleanup("nope.com") is False
+
+    def test_has_report_returns_true_for_existing(self):
+        store = ReportStore.get_instance()
+        store.add_report(_sample_report("test.com"))
+        assert store.has_report("test.com", "rpt-001") is True
+
+    def test_has_report_returns_false_for_missing_report_id(self):
+        store = ReportStore.get_instance()
+        store.add_report(_sample_report("test.com"))
+        assert store.has_report("test.com", "rpt-999") is False
+
+    def test_has_report_returns_false_for_unknown_domain(self):
+        store = ReportStore.get_instance()
+        assert store.has_report("nobody.com", "rpt-001") is False
+
+    def test_delete_report_removes_report_and_updates_stats(self):
+        store = ReportStore.get_instance()
+        store.add_report(_sample_report("test.com"))
+
+        result = store.delete_report("test.com", "rpt-001")
+        assert result is True
+        # Domain should be gone entirely when no reports remain
+        assert "test.com" not in store.get_domains()
+
+    def test_delete_report_with_remaining_reports_recomputes_stats(self):
+        store = ReportStore.get_instance()
+        report_a = _sample_report("test.com")
+        report_a["report_id"] = "rpt-001"
+
+        report_b = _sample_report("test.com")
+        report_b["report_id"] = "rpt-002"
+        report_b["summary"] = {"total_count": 3, "passed_count": 1, "failed_count": 2}
+
+        store.add_report(report_a)
+        store.add_report(report_b)
+
+        assert store.get_domain_summary("test.com")["reports_processed"] == 2
+
+        result = store.delete_report("test.com", "rpt-001")
+        assert result is True
+
+        summary = store.get_domain_summary("test.com")
+        assert summary["reports_processed"] == 1
+        # Stats should now reflect only report_b
+        assert summary["total_count"] == 3
+        assert summary["passed_count"] == 1
+
+    def test_delete_report_nonexistent_returns_false(self):
+        store = ReportStore.get_instance()
+        assert store.delete_report("test.com", "rpt-999") is False
+
+    def test_delete_report_unknown_domain_returns_false(self):
+        store = ReportStore.get_instance()
+        assert store.delete_report("nobody.com", "rpt-001") is False
+
+    def test_recompute_stats_after_add(self):
+        """_recompute_domain_stats is called on add; compliance_rate must be correct."""
+        store = ReportStore.get_instance()
+        report = _sample_report("test.com")
+        report["summary"] = {"total_count": 10, "passed_count": 8, "failed_count": 2}
+        store.add_report(report)
+
+        summary = store.get_domain_summary("test.com")
+        assert summary["compliance_rate"] == 80.0