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/app/_layout.tsx

@@ -6,15 +6,16 @@ import {
   useFonts,
 } from "@expo-google-fonts/inter";
 import { QueryClient, QueryClientProvider } from "@tanstack/react-query";
-import { Stack } from "expo-router";
+import { router, Stack } from "expo-router";
 import * as SplashScreen from "expo-splash-screen";
 import React, { useEffect } from "react";
+import { Alert } from "react-native";
 import { GestureHandlerRootView } from "react-native-gesture-handler";
 import { KeyboardProvider } from "react-native-keyboard-controller";
 import { SafeAreaProvider } from "react-native-safe-area-context";
 
 import { ErrorBoundary } from "@/components/ErrorBoundary";
-import { PostizProvider } from "@/context/PostizContext";
+import { PostizProvider, usePostiz } from "@/context/PostizContext";
 import { useNotifications } from "@/hooks/useNotifications";
 
 SplashScreen.preventAutoHideAsync();
@@ -33,6 +34,28 @@ function NotificationBootstrap() {
   return null;
 }
 
+function UnauthorizedHandler() {
+  const { unauthorized, clearUnauthorized } = usePostiz();
+  useEffect(() => {
+    if (!unauthorized) return;
+    Alert.alert(
+      "API key invalid",
+      "Your API key was rejected (401). Update it in Settings.",
+      [
+        {
+          text: "Open Settings",
+          onPress: () => {
+            clearUnauthorized();
+            router.push("/(tabs)/settings");
+          },
+        },
+        { text: "Dismiss", style: "cancel", onPress: clearUnauthorized },
+      ]
+    );
+  }, [unauthorized, clearUnauthorized]);
+  return null;
+}
+
 function RootLayoutNav() {
   return (
     <Stack screenOptions={{ headerBackTitle: "Back" }}>
@@ -63,6 +86,7 @@ export default function RootLayout() {
         <QueryClientProvider client={queryClient}>
           <PostizProvider>
             <NotificationBootstrap />
+            <UnauthorizedHandler />
             <GestureHandlerRootView style={{ flex: 1 }}>
               <KeyboardProvider>
                 <RootLayoutNav />