fix(ai): normalize OpenAI-compatible API base to /v1

Accept gateway root URLs like https://llm.example.com and auto-append /v1
so NewAPI-style providers work; update Extension AI help text accordingly.

inc/classes/class-aksrt-ai.php

@@ -62,7 +62,7 @@ class AKSRT_AI {
         $merged['enabled']    = !empty($merged['enabled']);
         $merged['provider']   = sanitize_key((string) ($merged['provider'] ?? self::PROVIDER_NONE));
         $merged['api_key']    = (string) ($merged['api_key'] ?? '');
-        $merged['api_base']   = esc_url_raw((string) ($merged['api_base'] ?? 'https://api.openai.com/v1'));
+        $merged['api_base']   = $this->normalize_api_base((string) ($merged['api_base'] ?? 'https://api.openai.com/v1'));
         $merged['model']      = sanitize_text_field((string) ($merged['model'] ?? 'gpt-3.5-turbo'));
         $merged['max_tokens'] = max(100, min(4000, (int) ($merged['max_tokens'] ?? 1000)));
         $merged['rate_limit'] = max(1, min(100, (int) ($merged['rate_limit'] ?? 10)));
@@ -294,11 +294,40 @@ class AKSRT_AI {
         }
     }
 
+    /**
+     * Normalize OpenAI-compatible base URL.
+     *
+     * Accepts gateway root (https://host), /v1, trailing slash, or full
+     * .../chat/completions and returns a base that can append /chat/completions.
+     */
+    public function normalize_api_base(string $api_base): string {
+        $api_base = trim($api_base);
+        if ($api_base === '') {
+            return 'https://api.openai.com/v1';
+        }
+
+        $api_base = esc_url_raw($api_base);
+        $api_base = rtrim($api_base, '/');
+
+        // If user pasted the full chat endpoint, strip the leaf.
+        if (preg_match('#/chat/completions$#i', $api_base)) {
+            $api_base = (string) preg_replace('#/chat/completions$#i', '', $api_base);
+            $api_base = rtrim($api_base, '/');
+        }
+
+        // Common gateways (NewAPI etc.): root host needs /v1.
+        if (!preg_match('#/(v1|openai/v1)$#i', $api_base)) {
+            $api_base .= '/v1';
+        }
+
+        return rtrim($api_base, '/');
+    }
+
     private function generate_via_theme(string $prompt, string $system, array $options): array {
         $config      = $this->get_config();
         $max_tokens  = (int) ($options['max_tokens'] ?? $config['max_tokens']);
         $temperature = (float) ($options['temperature'] ?? 0.7);
-        $api_base    = rtrim((string) $config['api_base'], '/');
+        $api_base    = $this->normalize_api_base((string) $config['api_base']);
 
         $response = wp_remote_post($api_base . '/chat/completions', [
             'headers' => [