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/useSync.ts

@@ -0,0 +1,102 @@
+/**
+ * Hook for managing offline sync with local SQLite cache.
+ */
+
+import { useEffect, useState, useCallback, useRef } from "react";
+import { useConvex } from "convex/react";
+import { createSyncService, type SyncService, type SyncStatus } from "../db/syncService";
+import { useHashCache } from "../context";
+
+/**
+ * Hook to manage sync service lifecycle and status.
+ * Initializes local database, syncs with Convex, and provides hashes for recognition.
+ */
+export function useSync() {
+  const convex = useConvex();
+  const syncServiceRef = useRef<SyncService | null>(null);
+  const [status, setStatus] = useState<SyncStatus>({
+    isInitialized: false,
+    isSyncing: false,
+    lastSync: 0,
+    localCardCount: 0,
+  });
+  
+  const { setCardHashes } = useHashCache();
+
+  // Initialize sync service
+  useEffect(() => {
+    if (!convex || syncServiceRef.current) return;
+
+    const service = createSyncService(convex);
+    syncServiceRef.current = service;
+
+    // Subscribe to status changes
+    const unsubscribe = service.onStatusChange(setStatus);
+
+    // Initialize and load cached hashes
+    const init = async () => {
+      await service.initialize();
+      
+      // Load cached hashes into app store
+      const hashes = await service.getHashes();
+      if (hashes.length > 0) {
+        setCardHashes(hashes);
+        console.log(`[useSync] Loaded ${hashes.length} cached hashes`);
+      }
+      
+      // Start background sync
+      service.sync().then(async () => {
+        // Reload hashes after sync
+        const updatedHashes = await service.getHashes();
+        setCardHashes(updatedHashes);
+      });
+    };
+
+    init();
+
+    return () => {
+      unsubscribe();
+    };
+  }, [convex, setCardHashes]);
+
+  // Manual sync trigger
+  const sync = useCallback(async () => {
+    if (!syncServiceRef.current) return;
+    
+    await syncServiceRef.current.sync();
+    
+    // Reload hashes after sync
+    const hashes = await syncServiceRef.current.getHashes();
+    setCardHashes(hashes);
+  }, [setCardHashes]);
+
+  // Clear local cache
+  const clearCache = useCallback(async () => {
+    if (!syncServiceRef.current) return;
+    
+    await syncServiceRef.current.clearLocalCache();
+    setCardHashes([]);
+  }, [setCardHashes]);
+
+  // Get current hashes from cache
+  const getHashes = useCallback(async () => {
+    if (!syncServiceRef.current) return [];
+    return syncServiceRef.current.getHashes();
+  }, []);
+
+  return {
+    ...status,
+    sync,
+    clearCache,
+    getHashes,
+  };
+}
+
+/**
+ * Context-free sync initialization for use in _layout.tsx
+ * Returns a component that initializes sync when mounted.
+ */
+export function SyncInitializer() {
+  useSync();
+  return null;
+}