fix(admin): join REST URLs correctly under plain permalinks

When permalink_structure is empty, rest_url() is
index.php?rest_route=/aksrt/v1. Naive base+endpoint produced
rest_route=/aksrt/v1/banners?kind=banner (query inside route value),
so WP returned rest_no_route and Banner/Hero managers 404'd.
Fold path into rest_route and append extra params as siblings.

assets/admin/src/api/index.js

@@ -1,7 +1,8 @@
 /**
  * AKSRT Admin API Client
  *
- * Communicates with the WordPress REST API at /wp-json/aksrt/v1.
+ * Communicates with the WordPress REST API at /wp-json/aksrt/v1
+ * (or index.php?rest_route=/aksrt/v1 when pretty permalinks are off).
  * Methods are organized into domain modules while the client keeps the shared
  * request pipeline and schema-domain normalization contract.
  */
@@ -15,6 +16,73 @@ function normalizeDomainKey(domain) {
   return String(domain || 'global').trim().replace(/-/g, '_')
 }
 
+/**
+ * Join REST base + endpoint correctly for both pretty and plain permalinks.
+ *
+ * Pretty:  https://site/wp-json/aksrt/v1 + /banners?kind=x
+ *       →  https://site/wp-json/aksrt/v1/banners?kind=x
+ *
+ * Plain:   https://site/index.php?rest_route=/aksrt/v1 + /banners?kind=x
+ *       →  https://site/index.php?rest_route=/aksrt/v1/banners&kind=x
+ *          (must NOT produce rest_route=/aksrt/v1/banners?kind=x)
+ *
+ * @param {string} baseUrl
+ * @param {string} endpoint path starting with /, may include ?query
+ * @returns {string}
+ */
+function joinRestUrl(baseUrl, endpoint) {
+  let path = endpoint == null || endpoint === '' ? '/' : String(endpoint)
+  let extraQuery = ''
+  const qIdx = path.indexOf('?')
+  if (qIdx !== -1) {
+    extraQuery = path.slice(qIdx + 1)
+    path = path.slice(0, qIdx)
+  }
+  if (!path.startsWith('/')) {
+    path = '/' + path
+  }
+
+  const base = String(baseUrl || '').trim() || '/wp-json/aksrt/v1'
+
+  // Plain permalinks: rest_route query mode
+  if (base.includes('rest_route=')) {
+    let u
+    try {
+      u = new URL(base, typeof window !== 'undefined' ? window.location.origin : 'https://localhost')
+    } catch {
+      // Fallback: naive append (should not hit with valid rest_url)
+      return base.replace(/\/?$/, '') + path + (extraQuery ? (base.includes('?') ? '&' : '?') + extraQuery : '')
+    }
+
+    const baseRoute = (u.searchParams.get('rest_route') || '/aksrt/v1').replace(/\/$/, '') || '/aksrt/v1'
+    let fullRoute
+    if (path === '/') {
+      fullRoute = baseRoute
+    } else if (path.startsWith('/aksrt/')) {
+      fullRoute = path
+    } else {
+      fullRoute = baseRoute + path
+    }
+    u.searchParams.set('rest_route', fullRoute)
+
+    if (extraQuery) {
+      const extra = new URLSearchParams(extraQuery)
+      extra.forEach((v, k) => {
+        u.searchParams.set(k, v)
+      })
+    }
+    return u.toString()
+  }
+
+  // Pretty /wp-json mode
+  const root = base.replace(/\/$/, '')
+  let url = root + (path === '/' ? '' : path)
+  if (extraQuery) {
+    url += (url.includes('?') ? '&' : '?') + extraQuery
+  }
+  return url
+}
+
 class ApiClient {
   constructor() {
     this.baseUrl = API_ROOT
@@ -58,11 +126,13 @@ class ApiClient {
       endpoint = endpoint.replace('/aksrt/v1', '') || '/'
     }
 
-    let url = `${this.baseUrl}${endpoint}`
+    let url = joinRestUrl(this.baseUrl, endpoint)
 
     if (params && typeof params === 'object') {
       const qs = new URLSearchParams(params).toString()
-      if (qs) url += (url.includes('?') ? '&' : '?') + qs
+      if (qs) {
+        url += (url.includes('?') ? '&' : '?') + qs
+      }
     }
 
     let finalBody = body
@@ -116,5 +186,5 @@ class ApiClient {
 
 Object.assign(ApiClient.prototype, apiMethods)
 
-export { normalizeDomainKey }
+export { normalizeDomainKey, joinRestUrl }
 export default new ApiClient()