Keep logs for a set number of days

Logs grew forever. A daily prune-logs cron now deletes entries older
than the app setting logs_keep_days (Settings > General, super admin;
default AppData.LogsKeepDays, 90), with an index on logs.created_at.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

src/functions/backend/db/app-settings/grab-logs-keep-days.ts

@@ -0,0 +1,30 @@
+import { AppData } from "@/src/data/app-data";
+import { LogsKeepDaysSettingKey } from "@/src/dict/log-categories";
+import type { LogRetentionOverview } from "@/src/types";
+import readStepLimit from "@/src/utils/read-step-limit";
+import grabAppSetting from "./grab-app-setting";
+
+/**
+ * How many days logs are kept: the install's own number (`logs_keep_days`,
+ * Settings > General), else `AppData.LogsKeepDays`.
+ */
+export async function grabLogsKeepDays() {
+    return readStepLimit({
+        saved: await grabAppSetting({ key: LogsKeepDaysSettingKey }),
+        fallback: AppData.LogsKeepDays,
+        max: AppData.LogsKeepDaysMax,
+    });
+}
+
+/**
+ * The number with its default and ceiling, for the settings page.
+ */
+export default async function grabLogRetentionOverview() {
+    const overview: LogRetentionOverview = {
+        keep_days: await grabLogsKeepDays(),
+        default_days: AppData.LogsKeepDays,
+        max: AppData.LogsKeepDaysMax,
+    };
+
+    return overview;
+}