feat(devices): manually add a device by MAC (offline pre-register) → 2.1.3

'+ Add by MAC' in the band header → POST /api/devices → lan_devices.addManual
(status=known, present=false; enriched on next scan). Repo + API + frontend tests.

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

lib/db/repos/lan_devices.js

@@ -19,6 +19,21 @@ export async function get(mac) {
   return r || null;
 }
 
+// Manually add a device by MAC (e.g. an offline device whose MAC you know). Lands
+// as status='known', present=false. Idempotent — re-adding updates name/grp/vendor.
+export async function addManual({ mac, name = null, grp = 'Flagged', vendor = null, randomized = false }) {
+  const { rows: [r] } = await pool.query(
+    `INSERT INTO lan_devices (mac, name, grp, vendor, randomized, status, present, first_seen, last_seen)
+     VALUES ($1,$2,$3,$4,$5,'known',false,now(),now())
+     ON CONFLICT (mac) DO UPDATE SET
+       name = EXCLUDED.name, grp = EXCLUDED.grp,
+       vendor = COALESCE(NULLIF(EXCLUDED.vendor,''), lan_devices.vendor),
+       status = 'known'
+     RETURNING ${COLS}`,
+    [mac, name, grp, vendor, !!randomized]);
+  return r;
+}
+
 // Insert unseen MACs as status='new'; for existing, refresh ip/vendor/last_seen/present
 // WITHOUT touching owner-curated name/grp/status/flagged.
 export async function upsertScan(rows) {