feat: add Timmy Chat mobile app (Expo/React Native)

- Single-screen chat interface with Timmy's sovereign AI personality
- Text messaging with real-time AI responses via server chat API
- Voice recording and playback with waveform visualization
- Image sharing (camera + photo library) with full-screen viewer
- File attachments via document picker
- Dark arcane theme matching the Timmy Time dashboard
- Custom app icon with glowing T circuit design
- Timmy system prompt ported from dashboard prompts.py
- Unit tests for chat utilities and message types

mobile-app/components/image-viewer.tsx

@@ -0,0 +1,54 @@
+import { Modal, View, Image, StyleSheet, StatusBar } from "react-native";
+import Pressable from "@/components/ui/pressable-fix";
+import MaterialIcons from "@expo/vector-icons/MaterialIcons";
+
+interface ImageViewerProps {
+  uri: string | null;
+  onClose: () => void;
+}
+
+export function ImageViewer({ uri, onClose }: ImageViewerProps) {
+  if (!uri) return null;
+
+  return (
+    <Modal visible animationType="fade" transparent statusBarTranslucent>
+      <View style={styles.overlay}>
+        <StatusBar barStyle="light-content" />
+        <Image source={{ uri }} style={styles.image} resizeMode="contain" />
+        <Pressable
+          onPress={onClose}
+          style={({ pressed }: { pressed: boolean }) => [
+            styles.closeBtn,
+            pressed && { opacity: 0.6 },
+          ]}
+        >
+          <MaterialIcons name="close" size={28} color="#fff" />
+        </Pressable>
+      </View>
+    </Modal>
+  );
+}
+
+const styles = StyleSheet.create({
+  overlay: {
+    flex: 1,
+    backgroundColor: "rgba(0,0,0,0.95)",
+    justifyContent: "center",
+    alignItems: "center",
+  },
+  image: {
+    width: "100%",
+    height: "80%",
+  },
+  closeBtn: {
+    position: "absolute",
+    top: 50,
+    right: 20,
+    width: 40,
+    height: 40,
+    borderRadius: 20,
+    backgroundColor: "rgba(255,255,255,0.15)",
+    alignItems: "center",
+    justifyContent: "center",
+  },
+});