feat: migrate icons to SF Symbols, refactor explore tab, add collections/programs data layer

- Replace all Ionicons with native SF Symbols via expo-symbols SymbolView
- Create reusable Icon wrapper component (src/shared/components/Icon.tsx)
- Remove @expo/vector-icons and lucide-react dependencies
- Refactor explore tab with filters, search, and category browsing
- Add collections and programs data with Supabase integration
- Add explore filter store and filter sheet
- Update i18n strings (en, de, es, fr) for new explore features
- Update test mocks and remove stale snapshots
- Add user fitness level to user store and types

app/_layout.tsx

@@ -153,6 +153,15 @@ function RootLayoutInner() {
                 animation: 'fade',
               }}
             />
+            <Stack.Screen
+              name="explore-filters"
+              options={{
+                presentation: 'formSheet',
+                headerShown: false,
+                sheetGrabberVisible: true,
+                sheetAllowedDetents: [0.5],
+              }}
+            />
           </Stack>
       </View>
     </QueryClientProvider>