fix(alerts): backend hardening + complete ACKNOWLEDGED migration

- new AlertInstanceRepository.filterInEnvLive(ids, env): single-query bulk ID validation
- AlertController.inEnvLiveIds now one SQL round-trip instead of N
- bulkMarkRead SQL: defense-in-depth AND deleted_at IS NULL
- bulkAck SQL already had deleted_at IS NULL guard — no change needed
- PostgresAlertInstanceRepositoryIT: add filterInEnvLive_excludes_other_env_and_soft_deleted
- V12MigrationIT: remove alert_reads assertion (table dropped by V17)

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

cameleer-server-app/src/test/java/com/cameleer/server/app/alerting/storage/PostgresAlertInstanceRepositoryIT.java

@@ -372,6 +372,18 @@ class PostgresAlertInstanceRepositoryIT extends AbstractPostgresIT {
         assertThat(rows).extracting(AlertInstance::id).contains(inst.id());
     }
 
+    @Test
+    void filterInEnvLive_excludes_other_env_and_soft_deleted() {
+        var a = insertFreshFiring();                        // env envId, live
+        var b = insertFreshFiring();                        // env envId, will be soft-deleted
+        repo.softDelete(b.id(), Instant.now());
+
+        UUID unknownId = UUID.randomUUID();                 // not in DB at all
+
+        var kept = repo.filterInEnvLive(List.of(a.id(), b.id(), unknownId), envId);
+        assertThat(kept).containsExactly(a.id());
+    }
+
     // -------------------------------------------------------------------------
 
     /** Creates and saves a fresh FIRING instance targeted at the test userId with its own rule. */

cameleer-server-app/src/test/java/com/cameleer/server/app/alerting/storage/V12MigrationIT.java

@@ -22,14 +22,15 @@ class V12MigrationIT extends AbstractPostgresIT {
 
     @Test
     void allAlertingTablesAndEnumsExist() {
+        // Note: alert_reads was created in V12 but dropped by V17 (superseded by read_at column).
         var tables = jdbcTemplate.queryForList(
             "SELECT table_name FROM information_schema.tables WHERE table_schema='public' " +
             "AND table_name IN ('alert_rules','alert_rule_targets','alert_instances'," +
-            "'alert_silences','alert_notifications','alert_reads')",
+            "'alert_silences','alert_notifications')",
             String.class);
         assertThat(tables).containsExactlyInAnyOrder(
             "alert_rules","alert_rule_targets","alert_instances",
-            "alert_silences","alert_notifications","alert_reads");
+            "alert_silences","alert_notifications");
 
         var enums = jdbcTemplate.queryForList(
             "SELECT typname FROM pg_type WHERE typname IN " +