feat: add navigation with tab bar and screen layouts

Expo Router file-based navigation with glass tab bar,
3 tabs (Créations, Explorer, Profil), Phosphor icons,
modal picker, and fade transitions.

app/(tabs)/explore.tsx

@@ -0,0 +1,60 @@
+import { StyleSheet, Text, View } from "react-native";
+import { useSafeAreaInsets } from "react-native-safe-area-context";
+import Animated, { FadeInDown } from "react-native-reanimated";
+import { GlassCard } from "@/components/glass";
+import { colors, typography, spacing, layout } from "@/theme";
+
+export default function ExploreScreen() {
+  const insets = useSafeAreaInsets();
+
+  return (
+    <View style={[styles.container, { paddingTop: insets.top + spacing.md }]}>
+      <Animated.View entering={FadeInDown.duration(500)}>
+        <GlassCard variant="subtle" radius="lg" padding={16}>
+          <Text style={typography.title}>Explorer</Text>
+          <Text style={[typography.caption, { marginTop: 2 }]}>
+            Découvrez la communauté
+          </Text>
+        </GlassCard>
+      </Animated.View>
+
+      <Animated.View
+        entering={FadeInDown.delay(200).duration(600)}
+        style={styles.placeholder}
+      >
+        <GlassCard variant="medium" radius="xl" padding={32}>
+          <View style={styles.content}>
+            <Text style={[typography.heading, { textAlign: "center" }]}>
+              Bientôt disponible
+            </Text>
+            <Text
+              style={[
+                typography.bodySecondary,
+                { textAlign: "center", marginTop: 8 },
+              ]}
+            >
+              Partagez vos créations et découvrez{"\n"}
+              celles de la communauté — V1.5
+            </Text>
+          </View>
+        </GlassCard>
+      </Animated.View>
+    </View>
+  );
+}
+
+const styles = StyleSheet.create({
+  container: {
+    flex: 1,
+    backgroundColor: colors.background,
+    paddingHorizontal: layout.screenPadding,
+  },
+  placeholder: {
+    flex: 1,
+    justifyContent: "center",
+    paddingHorizontal: spacing.md,
+  },
+  content: {
+    alignItems: "center",
+  },
+});