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/context/HashCacheContext.tsx

@@ -0,0 +1,64 @@
+/**
+ * React Context for card hash cache.
+ * Provides offline-first hash data for card recognition.
+ */
+
+import React, { createContext, useContext, useState, useCallback, type ReactNode } from "react";
+import type { CardHashEntry } from "../recognition";
+
+interface HashCacheState {
+  cardHashes: CardHashEntry[];
+  hashesLoaded: boolean;
+  lastHashSync: number;
+}
+
+interface HashCacheContextValue extends HashCacheState {
+  setCardHashes: (hashes: CardHashEntry[]) => void;
+  clearHashes: () => void;
+}
+
+const HashCacheContext = createContext<HashCacheContextValue | null>(null);
+
+export function HashCacheProvider({ children }: { children: ReactNode }) {
+  const [state, setState] = useState<HashCacheState>({
+    cardHashes: [],
+    hashesLoaded: false,
+    lastHashSync: 0,
+  });
+
+  const setCardHashes = useCallback((hashes: CardHashEntry[]) => {
+    setState({
+      cardHashes: hashes,
+      hashesLoaded: true,
+      lastHashSync: Date.now(),
+    });
+  }, []);
+
+  const clearHashes = useCallback(() => {
+    setState({
+      cardHashes: [],
+      hashesLoaded: false,
+      lastHashSync: 0,
+    });
+  }, []);
+
+  return (
+    <HashCacheContext.Provider
+      value={{
+        ...state,
+        setCardHashes,
+        clearHashes,
+      }}
+    >
+      {children}
+    </HashCacheContext.Provider>
+  );
+}
+
+export function useHashCache() {
+  const context = useContext(HashCacheContext);
+  if (!context) {
+    throw new Error("useHashCache must be used within HashCacheProvider");
+  }
+  return context;
+}