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>

convex/users.ts

@@ -0,0 +1,20 @@
+/**
+ * User queries and mutations using Convex Auth.
+ */
+
+import { query } from "./_generated/server";
+import { getAuthUserId } from "@convex-dev/auth/server";
+
+/**
+ * Get the currently authenticated user.
+ */
+export const me = query({
+  args: {},
+  handler: async (ctx) => {
+    const userId = await getAuthUserId(ctx);
+    if (!userId) {
+      return null;
+    }
+    return await ctx.db.get(userId);
+  },
+});