fix(rotate): record PPSK rotation password + sync banded-SSID siblings

Three bugs reported from prod after a PPSK rotation:

1. unifi.password_rotation.last_password was only saved after a
   whole-SSID rotation. PPSK-only setups (the typical guest-WiFi case)
   ran a successful rotation but the setting stayed empty, so the
   Settings → Tasks UI never showed the current password and the
   /api/unifi/wifi/current-password endpoint returned 404
   "no rotated password recorded yet". The PPSK loop now writes
   last_password on every successful PPSK rotation.

2. When an SSID is "banded" (band-steering disabled), UniFi splits it
   into one wlanconf per band — 2.4GHz and 5GHz each get their own _id
   and their own embedded PPSK array. Rotating the PPSK on one band
   left the other band with the old password. New
   UnifiApiClient::getWlanSiblings($wlanId) finds all wlanconfs that
   share an SSID name; both rotation and the manual modal edit now
   call updateEmbeddedPpsk on each sibling and update the matching
   UnifiPpsk DB rows.

3. The manual WiFi modal edit had the same band-blindness as #2 —
   editing the GUEST PPSK on the 2.4GHz half left the 5GHz half stale.
   WifiController::ppskUpdate now walks siblings the same way.

v1.8.1.

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

src/Services/UnifiApiClient.php

@@ -312,6 +312,40 @@ class UnifiApiClient
         return $this->put("/rest/wlanconf/{$wlanId}", $data);
     }
 
+    /**
+     * Find sibling WLAN configs — same SSID name, different _id. UniFi
+     * splits a "banded" SSID (band-steering disabled) into one wlanconf
+     * per band, each with its own _id and its own embedded PPSK array.
+     * A rotation that updates one band must also update the others, or
+     * the SSID's two halves drift out of sync.
+     *
+     * Returns an array of sibling wlan IDs (excludes $wlanId itself).
+     * Empty array if the target WLAN is unique or can't be found.
+     */
+    public function getWlanSiblings(string $wlanId): array
+    {
+        try {
+            $all = $this->get('/rest/wlanconf');
+        } catch (\Throwable) {
+            return [];
+        }
+
+        $target = null;
+        foreach ($all as $w) {
+            if (($w['_id'] ?? null) === $wlanId) { $target = $w; break; }
+        }
+        if (! $target || empty($target['name'])) return [];
+
+        $siblings = [];
+        foreach ($all as $w) {
+            if (($w['_id'] ?? null) === $wlanId) continue;
+            if (($w['name'] ?? null) === $target['name']) {
+                $siblings[] = $w['_id'];
+            }
+        }
+        return $siblings;
+    }
+
     // ── PPSK ─────────────────────────────────────────────────────────────────
 
     /**