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/recognition/skiaDecoder.ts

@@ -0,0 +1,121 @@
+/**
+ * Skia-based image decoder for getting RGBA pixel data.
+ * Uses react-native-skia to decode images and extract pixel buffers.
+ */
+
+import {
+  Skia,
+  useImage,
+  SkImage,
+} from "@shopify/react-native-skia";
+
+/**
+ * Decode a base64 PNG/JPEG image and return RGBA pixel data.
+ *
+ * @param base64 - Base64 encoded image data (without data URI prefix)
+ * @returns RGBA pixel data with dimensions
+ */
+export function decodeImageBase64(base64: string): {
+  pixels: Uint8Array;
+  width: number;
+  height: number;
+} | null {
+  try {
+    // Decode base64 to data
+    const data = Skia.Data.fromBase64(base64);
+    if (!data) return null;
+
+    // Create image from data
+    const image = Skia.Image.MakeImageFromEncoded(data);
+    if (!image) return null;
+
+    const width = image.width();
+    const height = image.height();
+
+    // Read pixels from the image
+    // Note: Skia images are in RGBA format
+    const pixels = image.readPixels(0, 0, {
+      width,
+      height,
+      colorType: 4, // RGBA_8888
+      alphaType: 1, // Unpremultiplied
+    });
+
+    if (!pixels) return null;
+
+    return {
+      pixels: new Uint8Array(pixels),
+      width,
+      height,
+    };
+  } catch (error) {
+    console.error("[SkiaDecoder] Failed to decode image:", error);
+    return null;
+  }
+}
+
+/**
+ * Decode an image from a file URI and return RGBA pixel data.
+ *
+ * @param uri - File URI (e.g., file:///path/to/image.png)
+ * @returns Promise with RGBA pixel data
+ */
+export async function decodeImageFromUri(uri: string): Promise<{
+  pixels: Uint8Array;
+  width: number;
+  height: number;
+} | null> {
+  try {
+    // Fetch the image data
+    const response = await fetch(uri);
+    const arrayBuffer = await response.arrayBuffer();
+    const base64 = arrayBufferToBase64(arrayBuffer);
+
+    return decodeImageBase64(base64);
+  } catch (error) {
+    console.error("[SkiaDecoder] Failed to load image from URI:", error);
+    return null;
+  }
+}
+
+/**
+ * Convert ArrayBuffer to base64 string.
+ */
+function arrayBufferToBase64(buffer: ArrayBuffer): string {
+  let binary = "";
+  const bytes = new Uint8Array(buffer);
+  const len = bytes.byteLength;
+  for (let i = 0; i < len; i++) {
+    binary += String.fromCharCode(bytes[i]);
+  }
+  return btoa(binary);
+}
+
+/**
+ * React hook to decode an image from URI.
+ * Uses Skia's useImage hook for caching.
+ */
+export function useDecodedImage(uri: string | null) {
+  const skiaImage = useImage(uri);
+
+  if (!skiaImage) {
+    return { loading: true, pixels: null, width: 0, height: 0 };
+  }
+
+  const width = skiaImage.width();
+  const height = skiaImage.height();
+
+  const pixels = skiaImage.readPixels(0, 0, {
+    width,
+    height,
+    colorType: 4, // RGBA_8888
+    alphaType: 1, // Unpremultiplied
+  });
+
+  return {
+    loading: false,
+    pixels: pixels ? new Uint8Array(pixels) : null,
+    width,
+    height,
+  };
+}