fix: align POST /posts payload with Postiz public API v1 format

Switch from deprecated content/integrations structure to posts[] array
with integration.id and value[] fields. Add required shortLink and tags
fields. Use globalThis.fetch instead of axios for the POST request.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

artifacts/postiz-mobile/app/(tabs)/compose.tsx

@@ -1,6 +1,5 @@
 import { Feather } from "@expo/vector-icons";
 import { useQuery, useQueryClient } from "@tanstack/react-query";
-import axios from "axios";
 import DateTimePicker from "@react-native-community/datetimepicker";
 import * as Haptics from "expo-haptics";
 import { Image } from "expo-image";
@@ -111,7 +110,7 @@ export default function ComposeScreen() {
   };
 
   const handleSubmit = async () => {
-    if (!client) return;
+    if (!isConfigured) return;
     if (!content.trim()) {
       Alert.alert("Empty post", "Please write something before posting.");
       return;
@@ -130,18 +129,39 @@ export default function ComposeScreen() {
           media = [{ id: uploaded.id, path: uploaded.path }];
         }
       }
-      const contentItem: { content: string; image?: Array<{ id: string; path: string }> } = {
-        content: content.trim(),
-      };
-      if (media.length > 0) contentItem.image = media;
-
       const payload = {
         type: postNow ? "now" : "schedule",
         date: postNow ? new Date().toISOString() : scheduleDate.toISOString(),
-        content: [contentItem],
+        shortLink: false,
-        integrations: selectedChannels,
+        tags: [] as string[],
+        posts: selectedChannels.map((integrationId) => ({
+          integration: { id: integrationId },
+          value: [{ content: content.trim(), id: "", image: media }],
+        })),
       };
-      await client.post("posts", payload);
+      const body = JSON.stringify(payload);
+
+      // eslint-disable-next-line no-undef
+      const res = await globalThis.fetch(`${baseUrl}/posts`, {
+        method: "POST",
+        headers: {
+          Authorization: apiKey,
+          "Content-Type": "application/json",
+        },
+        body,
+      });
+
+      if (!res.ok) {
+        let detail = "";
+        try {
+          const raw = await res.text();
+          detail = raw.slice(0, 300);
+        } catch {
+          detail = res.statusText;
+        }
+        throw new Error(`HTTP ${res.status}: ${detail}`);
+      }
+
       Haptics.notificationAsync(Haptics.NotificationFeedbackType.Success);
       Alert.alert(
         "Posted!",
@@ -152,16 +172,7 @@ export default function ComposeScreen() {
       queryClient.invalidateQueries({ queryKey: ["posts-list"] });
     } catch (e: unknown) {
       Haptics.notificationAsync(Haptics.NotificationFeedbackType.Error);
-      let msg = "Could not submit post.";
+      const msg = e instanceof Error ? e.message : "Could not submit post.";
-      if (axios.isAxiosError(e)) {
-        const data = e.response?.data;
-        const detail = data
-          ? (typeof data === "string" ? data : (data?.message ?? data?.error ?? JSON.stringify(data))).toString().slice(0, 300)
-          : e.message;
-        msg = `HTTP ${e.response?.status ?? "?"}: ${detail}`;
-      } else if (e instanceof Error) {
-        msg += `\n${e.message}`;
-      }
       Alert.alert("Failed", msg);
     } finally {
       setSubmitting(false);