feat(sv): Backups card — offsite DR status (Core-4 -> Farm) + /api/backups (2.6.0)

migration 026 backup_runs; POST ingest (owner) from offsite-backup.sh, GET for the
Sacred Valley card showing last run, per-guest sizes, Farm free, schedule.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

lib/db/repos/backups.js

@@ -0,0 +1,21 @@
+import { pool } from '../pool.js';
+
+export async function record({ ok = true, total_bytes = null, won_free_bytes = null,
+                               guests = null, duration_sec = null }) {
+  const { rows: [r] } = await pool.query(
+    `INSERT INTO backup_runs (ok, total_bytes, won_free_bytes, guests, duration_sec)
+     VALUES ($1,$2,$3,$4,$5) RETURNING *`,
+    [ok, total_bytes, won_free_bytes, guests ? JSON.stringify(guests) : null, duration_sec]);
+  return r;
+}
+
+export async function latest() {
+  const { rows: [r] } = await pool.query(
+    `SELECT * FROM backup_runs ORDER BY id DESC LIMIT 1`);
+  return r || null;
+}
+
+export async function count() {
+  const { rows: [r] } = await pool.query(`SELECT count(*)::int AS n FROM backup_runs`);
+  return r.n;
+}