Mobile: bottom tab bar (Cards · Collectibles · Agents · Settings)

Restructure the app into an Expo Router (tabs) group with a bottom navbar:
- 🎒 Cards (bag-personal) = the gallery (moved from app/index.tsx).
- 💰 Collectibles (sack) + 🤖 Agents (robot) = new empty-state screens.
- ⚙️ Settings (cog) = demo settings (app info + Clear all cards).
Root stack hides the (tabs) header; removed the Phase-1 (tabs)/cards.tsx and
pointed the dormant (auth)/login redirect at "/". localCardsStore gains clear().

Co-Authored-By: Claude Opus 4.8 (1M context) <[email protected]>

cardclaws-mobile/app/(tabs)/agents.tsx

@@ -0,0 +1,27 @@
+// Work-agent cards — AI agents attached to your cards. None yet; this is their
+// home.
+import { MaterialCommunityIcons } from "@expo/vector-icons";
+import { StyleSheet, Text, View } from "react-native";
+import { useSafeAreaInsets } from "react-native-safe-area-context";
+
+export default function Agents() {
+  const insets = useSafeAreaInsets();
+  return (
+    <View style={[styles.root, { paddingTop: insets.top }]}>
+      <View style={styles.center}>
+        <MaterialCommunityIcons name="robot" size={48} color="#3a3a44" />
+        <Text style={styles.title}>No agent cards yet</Text>
+        <Text style={styles.hint}>
+          Cards backed by an AI work agent will appear here.
+        </Text>
+      </View>
+    </View>
+  );
+}
+
+const styles = StyleSheet.create({
+  root: { flex: 1, backgroundColor: "#0a0a0c" },
+  center: { flex: 1, alignItems: "center", justifyContent: "center", padding: 32, gap: 10 },
+  title: { color: "#f5f5f7", fontSize: 20, fontWeight: "700" },
+  hint: { color: "#6b6b70", fontSize: 14, textAlign: "center", lineHeight: 20 },
+});