feat: multi-images, media library, + fix HTML in notifications

Multi-images (compose):
- Replace single imageUri with mediaItems: MediaItem[] (local | uploaded)
- allowsMultipleSelection: true, selectionLimit up to 4 total
- Each picked image is resized to max 1920px before upload
- Thumbnail row with individual × remove buttons
- uploaded badge (cloud icon) on library/prefill images
- buildMediaPayload() uploads local items, passes uploaded items as-is

Media Library:
- New MediaLibraryModal component — full-screen modal
- Fetches GET /media from Postiz instance
- 3-column grid with multi-select (capped at remaining slots)
- Selected items added to compose media pool

Notifications:
- Strip HTML from notification body text

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

artifacts/postiz-mobile/hooks/useNotifications.ts

@@ -2,6 +2,7 @@ import { useCallback, useEffect, useRef } from "react";
 import { Platform } from "react-native";
 import { usePostiz } from "@/context/PostizContext";
 import { PostizPost } from "@/context/PostizContext";
+import { stripHtml } from "@/lib/stripHtml";
 
 const POLL_INTERVAL_MS = 15 * 60 * 1000;
 const SEEN_KEY = "postiz_seen_statuses";
@@ -44,10 +45,7 @@ async function sendStatusNotification(post: PostizPost) {
     await Notifications.scheduleNotificationAsync({
       content: {
         title: isError ? "Post failed to publish" : "Post published!",
-        body:
-          post.content.length > 80
-            ? post.content.slice(0, 80) + "…"
-            : post.content,
+        body: (() => { const t = stripHtml(post.content); return t.length > 80 ? t.slice(0, 80) + "…" : t; })(),
         data: { postId: post.id },
       },
       trigger: null,