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/components/PostCard.tsx

@@ -12,6 +12,7 @@ import {
 import { Swipeable } from "react-native-gesture-handler";
 import { useColors } from "@/hooks/useColors";
 import { PostizPost } from "@/context/PostizContext";
+import { stripHtml } from "@/lib/stripHtml";
 import { StatusBadge } from "./StatusBadge";
 
 interface PostCardProps {
@@ -118,10 +119,11 @@ export function PostCard({ post, onDelete, onLongPress, onReschedule }: PostCard
       : undefined;
 
   const integrations = post.integrations ?? (post.integration ? [post.integration] : []);
+  const plainContent = stripHtml(post.content);
   const truncatedContent =
-    post.content.length > 140
-      ? post.content.slice(0, 140) + "…"
-      : post.content;
+    plainContent.length > 140
+      ? plainContent.slice(0, 140) + "…"
+      : plainContent;
 
   return (
     <Swipeable