feat: official Postiz icon + strip HTML from post content display

- Replace icon.png with official Postiz logo (1024x1024, generated from
  upstream postiz.svg at gitroomhq/postiz-app)
- Add lib/stripHtml.ts: converts <br>/<p> to newlines, strips all tags,
  decodes HTML entities
- PostCard: use stripHtml on content before truncation and display
- posts.tsx: use stripHtml for context menu preview and clipboard copy
  (API payloads keep original HTML for retry/reschedule)

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

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

@@ -22,6 +22,7 @@ import { PostCard } from "@/components/PostCard";
 import { PostizPost, usePostiz } from "@/context/PostizContext";
 import { useColors } from "@/hooks/useColors";
 import { extractError } from "@/lib/extractError";
+import { stripHtml } from "@/lib/stripHtml";
 
 const SORT_STORAGE_KEY = "postiz_posts_sort";
 
@@ -193,14 +194,15 @@ export default function PostsScreen() {
   const showContextMenu = (post: PostizPost) => {
     Haptics.impactAsync(Haptics.ImpactFeedbackStyle.Medium);
 
-    const preview = post.content.slice(0, 60) + (post.content.length > 60 ? "…" : "");
+    const plain = stripHtml(post.content);
+    const preview = plain.slice(0, 60) + (plain.length > 60 ? "…" : "");
 
     const buttons: Array<{ text: string; style?: "cancel" | "destructive" | "default"; onPress?: () => void }> = [];
 
     buttons.push({
       text: "Copy text",
       onPress: async () => {
-        await Clipboard.setStringAsync(post.content);
+        await Clipboard.setStringAsync(stripHtml(post.content));
         Haptics.notificationAsync(Haptics.NotificationFeedbackType.Success);
         setCopyToast(true);
         setTimeout(() => setCopyToast(false), 2000);