feat(navigation): add tab bar icons using Ionicons

src/features/workout-builder/screens/BuilderScreen.tsx

@@ -93,7 +93,7 @@ export function BuilderScreen() {
                   keyboardType="numeric"
                   value={String(set.distancePerRep)}
                   onChangeText={(t) => updateSet(index, { distancePerRep: Number(t) || 0 })}
-                  className="bg-white border border-slate-300 rounded-lg px-3 py-2 text-slate-900 text-center"
+                  className="bg-white border border-slate-300 rounded-lg px-3 py-2 text-slate-900"
                 />
               </View>
               <View className="flex-1">
@@ -102,7 +102,7 @@ export function BuilderScreen() {
                   keyboardType="numeric"
                   value={String(set.repCount)}
                   onChangeText={(t) => updateSet(index, { repCount: Number(t) || 1 })}
-                  className="bg-white border border-slate-300 rounded-lg px-3 py-2 text-slate-900 text-center"
+                  className="bg-white border border-slate-300 rounded-lg px-3 py-2 text-slate-900"
                 />
               </View>
               <View className="flex-1">
@@ -111,7 +111,7 @@ export function BuilderScreen() {
                   keyboardType="numeric"
                   value={String(set.restDuration)}
                   onChangeText={(t) => updateSet(index, { restDuration: Number(t) || 0 })}
-                  className="bg-white border border-slate-300 rounded-lg px-3 py-2 text-slate-900 text-center"
+                  className="bg-white border border-slate-300 rounded-lg px-3 py-2 text-slate-900"
                 />
               </View>
             </View>

src/navigation/MainTabNavigator.tsx

@@ -1,4 +1,5 @@
 import { createBottomTabNavigator } from "@react-navigation/bottom-tabs";
+import { Ionicons } from "@expo/vector-icons";
 import { MainTabParamList } from "./types";
 import { WorkoutNavigator } from "./WorkoutNavigator";
 import { HistoryNavigator } from "./HistoryNavigator";
@@ -22,10 +23,9 @@ export function MainTabNavigator() {
         component={WorkoutNavigator}
         options={{
           headerShown: false,
-          tabBarIcon: ({ color, size }) => {
-            // Placeholder — replace with Expo vector icons later
-            return null;
-          },
+          tabBarIcon: ({ color, size }) => (
+            <Ionicons name="water" size={size} color={color} />
+          ),
         }}
       />
       <Tab.Screen
@@ -33,18 +33,18 @@ export function MainTabNavigator() {
         component={HistoryNavigator}
         options={{
           headerShown: false,
-          tabBarIcon: ({ color, size }) => {
-            return null;
-          },
+          tabBarIcon: ({ color, size }) => (
+            <Ionicons name="time-outline" size={size} color={color} />
+          ),
         }}
       />
       <Tab.Screen
         name="Settings"
         component={SettingsScreen}
         options={{
-          tabBarIcon: ({ color, size }) => {
-            return null;
-          },
+          tabBarIcon: ({ color, size }) => (
+            <Ionicons name="settings-outline" size={size} color={color} />
+          ),
         }}
       />
     </Tab.Navigator>