feat: UX improvements, security hardening, and code cleanup

- Extract shared extractError utility (lib/extractError.ts), remove 3 duplicate copies
- Export DEFAULT_BASE_URL from PostizContext, remove duplicate in settings
- Add 401 interceptor in axios client: fires UnauthorizedHandler in _layout → alert + redirect to Settings
- Calendar day items now tappable: tap opens context menu (Copy / Edit / Repost)
- Persist sort order (newest/oldest) across sessions via AsyncStorage
- Filter chips show post count per status (Queue 3, Error 1, etc.)
- Copy text action now shows a brief "Copied" toast + haptic feedback
- PostCard: swipe right → Reschedule action (QUEUE posts only, amber color)
- Compose: per-network char limit (Twitter 280, Instagram 2200…) with color warning at 90%
- Compose: local draft save/restore via AsyncStorage with restore banner on open
- Compose: prefillImagePath/prefillImageId params allow Edit/Repost to carry over existing media

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

artifacts/postiz-mobile/lib/extractError.ts

@@ -0,0 +1,20 @@
+import axios from "axios";
+
+export function extractError(err: unknown): string {
+  if (axios.isAxiosError(err)) {
+    const status = err.response?.status;
+    const data = err.response?.data;
+    if (data) {
+      const body =
+        typeof data === "string"
+          ? data.slice(0, 200)
+          : (data?.message ?? data?.error ?? JSON.stringify(data)).toString().slice(0, 200);
+      return status ? `HTTP ${status}: ${body}` : body;
+    }
+    if (status) return `HTTP ${status} — ${err.message}`;
+    if (err.code === "ECONNABORTED") return "Request timed out. Check that the URL is reachable.";
+    if (err.message) return err.message;
+  }
+  if (err instanceof Error) return err.message;
+  return "Unknown error";
+}