Let a super admin read the database from the app

A new super admin settings page, /admin/settings/database, lists every
table with its record count and size, and one page of the open table's
records newest key first. Values are cut inside SQL (400 characters, with
a flag saying so) and a record opens whole in a modal, so a table of long
texts reads without shipping it all. A search matches every column's
text, word by word or as a phrase, which is the one thing that also works
on a virtual table. Nothing in it writes: the catalog, the records and
the single record are all reads, GET only.

src/functions/backend/database/grab-table-catalog-entry.ts

@@ -0,0 +1,36 @@
+import AppError from "@/src/utils/app-error";
+import grabDatabaseTables from "./grab-database-tables";
+import type { DatabaseTableSummary } from "@/src/types";
+
+type Params = {
+    /**
+     * The table asked for, as it came in the query string. The first table
+     * is used when nothing is asked for.
+     */
+    table?: string | null;
+};
+
+/**
+ * One table, or the first one when nothing is asked for. Anything else is
+ * refused with a message safe to show: the browser only ever reads tables
+ * that are in the database, never a name it built itself.
+ */
+export default async function grabTableCatalogEntry({ table }: Params): Promise<DatabaseTableSummary> {
+    const tables = await grabDatabaseTables();
+
+    if (!tables.length) {
+        throw new AppError(`Couldn't read the database's tables.`);
+    }
+
+    const first = tables[0];
+
+    if (!table && first) return first;
+
+    const entry = tables.find((candidate) => candidate.name == table);
+
+    if (!entry) {
+        throw new AppError(`There's no table called "${table}".`);
+    }
+
+    return entry;
+}