test(observability): expand grafana_reader coverage with write-deny + PII negatives

The original 4 tests asserted SELECT existed on the three granted tables
and was absent on app_users. That left two gaps a future migration could
slip through silently:

- INSERT/UPDATE/DELETE on the granted tables — if someone GRANTed write
  access on, say, documents to grafana_reader, the SELECT positives stay
  green and the boundary is breached invisibly.
- Other PII / sensitive tables — the single app_users negative checks
  one table; a wildcard "GRANT SELECT ON ALL TABLES IN SCHEMA public"
  would still leave it green by accident if app_users wasn't the only
  sensitive table.

Switch to a hasPrivilege(table, privilege) helper, add three write-deny
tests (INSERT/UPDATE/DELETE on each granted table), and replace the
single app_users negative with a parameterized sweep over app_users,
user_groups, persons, notifications, document_comments,
document_annotations, geschichten. New sensitive tables get added to
that list as they appear.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

backend/src/test/java/org/raddatz/familienarchiv/config/GrafanaReaderRoleIntegrationTest.java

@@ -1,6 +1,8 @@
 package org.raddatz.familienarchiv.config;
 
 import org.junit.jupiter.api.Test;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.ValueSource;
 import org.raddatz.familienarchiv.PostgresContainerConfig;
 import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.boot.data.jpa.test.autoconfigure.DataJpaTest;
@@ -10,6 +12,9 @@ import org.springframework.jdbc.core.JdbcTemplate;
 
 import static org.assertj.core.api.Assertions.assertThat;
 
+// GRAFANA_DB_PASSWORD is supplied via the global test default in
+// src/test/resources/application.properties — FlywayConfig fails closed
+// when it is unset, so all tests that load the migration path need it.
 @DataJpaTest
 @AutoConfigureTestDatabase(replace = AutoConfigureTestDatabase.Replace.NONE)
 @Import({PostgresContainerConfig.class, FlywayConfig.class})
@@ -17,31 +22,68 @@ class GrafanaReaderRoleIntegrationTest {
 
     @Autowired JdbcTemplate jdbc;
 
+    // --- positive grants (SELECT on the three explicitly granted tables) ---
+
     @Test
     void grafana_reader_has_select_on_audit_log() {
-        assertThat(hasSelect("audit_log")).isTrue();
+        assertThat(hasPrivilege("audit_log", "SELECT")).isTrue();
     }
 
     @Test
     void grafana_reader_has_select_on_documents() {
-        assertThat(hasSelect("documents")).isTrue();
+        assertThat(hasPrivilege("documents", "SELECT")).isTrue();
     }
 
     @Test
     void grafana_reader_has_select_on_transcription_blocks() {
-        assertThat(hasSelect("transcription_blocks")).isTrue();
+        assertThat(hasPrivilege("transcription_blocks", "SELECT")).isTrue();
+    }
+
+    // --- write-deny on the granted tables: SELECT-only means SELECT-only.
+    // A future migration that GRANTs INSERT/UPDATE/DELETE on any of these
+    // would fail these tests, even though the original positive grants still
+    // pass. Locks the boundary in both directions.
+
+    @Test
+    void grafana_reader_has_no_INSERT_on_documents() {
+        assertThat(hasPrivilege("documents", "INSERT")).isFalse();
     }
 
     @Test
-    void grafana_reader_has_no_select_on_app_users() {
-        assertThat(hasSelect("app_users")).isFalse();
+    void grafana_reader_has_no_UPDATE_on_audit_log() {
+        assertThat(hasPrivilege("audit_log", "UPDATE")).isFalse();
     }
 
-    private boolean hasSelect(String table) {
+    @Test
+    void grafana_reader_has_no_DELETE_on_transcription_blocks() {
+        assertThat(hasPrivilege("transcription_blocks", "DELETE")).isFalse();
+    }
+
+    // --- negative grants: PII / sensitive tables MUST NOT be readable.
+    // The parameterized form catches the "someone widened the grant to
+    // ALL TABLES IN SCHEMA public" footgun — three specific positive grants
+    // would still pass while this sweep turns red.
+
+    @ParameterizedTest
+    @ValueSource(strings = {
+            "app_users",
+            "user_groups",
+            "persons",
+            "notifications",
+            "document_comments",
+            "document_annotations",
+            "geschichten"
+    })
+    void grafana_reader_has_no_SELECT_on_protected_table(String table) {
+        assertThat(hasPrivilege(table, "SELECT")).isFalse();
+    }
+
+    private boolean hasPrivilege(String table, String privilege) {
         Boolean result = jdbc.queryForObject(
-                "SELECT has_table_privilege('grafana_reader', ?, 'SELECT')",
+                "SELECT has_table_privilege('grafana_reader', ?, ?)",
                 Boolean.class,
-                table);
+                table,
+                privilege);
         return Boolean.TRUE.equals(result);
     }
 }