Sell PRO as an in-app unlock, take shared photos, and let FX run negative

- One free Play app (com.locphamtran.recipescamera) with an expo-iap PRO
  unlock, replacing the paid apk for the store channel
- Android SEND/SEND_MULTIPLE share target feeds photos into the editor,
  on cold start and on resume
- BACK button in the TopBar and press-and-hold PEEK replace the chip row
- NOISE REDUCTION and SHARPENING accept -10: a negative SHARPENING softens
  the frame before the grain pass, a negative NOISE REDUCTION re-grains it,
  in the Skia engine, the live preview and the Kotlin export path alike

src/components/TopBar.tsx

@@ -1,7 +1,7 @@
 import React, { useState } from 'react';
 import { View, Text, TouchableOpacity, TextInput, Modal, KeyboardAvoidingView, Platform, Alert } from 'react-native';
 import { useSafeAreaInsets } from 'react-native-safe-area-context';
-import { Plus, Pencil } from 'lucide-react-native';
+import { Plus, Pencil, Undo2 } from 'lucide-react-native';
 import * as Haptics from 'expo-haptics';
 
 interface TopBarProps {
@@ -16,9 +16,23 @@ interface TopBarProps {
   // SAVE & SHARE -> EXPORT: write this look to an encrypted recipe file and
   // hand it to the system share sheet so it can reach another phone.
   onExportShare: (name: string) => void;
+  // BACK (undo): one step back through the look's history. PRO only — App
+  // refuses and offers the paywall when a LITE build taps it. No count is
+  // drawn: the icon turns amber while there is a step to go back to.
+  onUndo: () => void;
+  undoDepth: number;
 }
 
-export default function TopBar({ mode, recipeName, onSaveRecipe, onOverwriteRecipe, onEditRecipe, onExportShare }: TopBarProps) {
+export default function TopBar({
+  mode,
+  recipeName,
+  onSaveRecipe,
+  onOverwriteRecipe,
+  onEditRecipe,
+  onExportShare,
+  onUndo,
+  undoDepth,
+}: TopBarProps) {
   const insets = useSafeAreaInsets();
   const [modalVisible, setModalVisible] = useState(false);
   const [newRecipeName, setNewRecipeName] = useState('');
@@ -75,6 +89,17 @@ export default function TopBar({ mode, recipeName, onSaveRecipe, onOverwriteReci
         </View>
 
         <View className="flex-row items-center space-x-2">
+          {/* BACK: the history control the chip row used to carry, sitting
+              between the status block and SAVE & SHARE. Lucide (ISC) vector
+              — no icon font to ship or license. */}
+          <TouchableOpacity
+            onPress={onUndo}
+            accessibilityLabel="BACK"
+            className="rounded-full border border-zinc-700/80 bg-black/45 p-2.5"
+            activeOpacity={0.7}
+          >
+            <Undo2 size={13} color={undoDepth > 0 ? '#f59e0b' : '#52525b'} />
+          </TouchableOpacity>
           {onEditRecipe && (
             <TouchableOpacity
               onPress={onEditRecipe}