Migrate from .NET MAUI to Expo + Convex

Complete rewrite of Scry using TypeScript stack:

- Expo/React Native with Expo Router (file-based routing)
- Convex backend (serverless functions + real-time database)
- Adaptive camera system (expo-camera in Expo Go, Vision Camera in production)
- React Native Skia + fast-opencv for image processing
- GDPR-compliant auth setup with Zitadel OIDC (pending configuration)

Key features:
- Card recognition pipeline ported to TypeScript
- Perceptual hashing (192-bit color pHash)
- CLAHE preprocessing for lighting normalization
- Local SQLite cache with Convex sync
- Collection management with offline support

Removes all .NET/MAUI code (src/, test/, tools/).

💘 Generated with Crush

Assisted-by: Claude Opus 4.5 via Crush <crush@charm.land>

lib/hooks/useCamera.ts

@@ -0,0 +1,116 @@
+/**
+ * Hook for camera permissions.
+ * Supports both expo-camera (Expo Go) and react-native-vision-camera (production).
+ */
+
+import { useState, useEffect, useRef } from "react";
+import { Platform, Linking, Alert } from "react-native";
+import Constants from "expo-constants";
+
+// Detect if running in Expo Go
+const isExpoGo = Constants.appOwnership === "expo";
+
+export interface CameraPermissionState {
+  hasPermission: boolean;
+  isLoading: boolean;
+  error: string | null;
+}
+
+/**
+ * Hook for camera permissions that works in both Expo Go and production builds.
+ */
+export function useCameraPermission(): CameraPermissionState & { requestPermission: () => Promise<void> } {
+  const [hasPermission, setHasPermission] = useState(false);
+  const [isLoading, setIsLoading] = useState(true);
+  const [error, setError] = useState<string | null>(null);
+
+  useEffect(() => {
+    checkPermission();
+  }, []);
+
+  const checkPermission = async () => {
+    try {
+      if (isExpoGo) {
+        // Use expo-camera
+        const { Camera } = await import("expo-camera");
+        const { status } = await Camera.getCameraPermissionsAsync();
+        setHasPermission(status === "granted");
+      } else {
+        // Use react-native-vision-camera
+        const { Camera } = await import("react-native-vision-camera");
+        const status = await Camera.getCameraPermissionStatus();
+        setHasPermission(status === "granted");
+      }
+    } catch (err) {
+      setError(err instanceof Error ? err.message : "Failed to check camera permission");
+    } finally {
+      setIsLoading(false);
+    }
+  };
+
+  const requestPermission = async () => {
+    try {
+      setIsLoading(true);
+      setError(null);
+
+      if (isExpoGo) {
+        // Use expo-camera
+        const { Camera } = await import("expo-camera");
+        const { status, canAskAgain } = await Camera.requestCameraPermissionsAsync();
+        
+        if (status === "granted") {
+          setHasPermission(true);
+        } else {
+          if (!canAskAgain) {
+            showSettingsAlert();
+          }
+          setError("Camera permission denied");
+        }
+      } else {
+        // Use react-native-vision-camera
+        const { Camera } = await import("react-native-vision-camera");
+        const status = await Camera.requestCameraPermission();
+        
+        if (status === "granted") {
+          setHasPermission(true);
+        } else if (status === "denied") {
+          showSettingsAlert();
+          setError("Camera permission denied");
+        }
+      }
+    } catch (err) {
+      setError(err instanceof Error ? err.message : "Failed to request camera permission");
+    } finally {
+      setIsLoading(false);
+    }
+  };
+
+  return { hasPermission, isLoading, error, requestPermission };
+}
+
+function showSettingsAlert() {
+  Alert.alert(
+    "Camera Permission Required",
+    "Scry needs camera access to scan cards. Please enable it in Settings.",
+    [
+      { text: "Cancel", style: "cancel" },
+      {
+        text: "Open Settings",
+        onPress: () => {
+          if (Platform.OS === "ios") {
+            Linking.openURL("app-settings:");
+          } else {
+            Linking.openSettings();
+          }
+        },
+      },
+    ]
+  );
+}
+
+/**
+ * Returns true if using expo-camera (Expo Go), false for Vision Camera (production).
+ */
+export function useIsExpoGo(): boolean {
+  return isExpoGo;
+}