feat: keep local relay connections alive in flight mode

- Add persistent keep-alive subscription for local relays
- Prevents disconnection when no other subscriptions are active
- Uses minimal subscription (kinds: [0], limit: 0) to keep connection open
- Properly cleans up subscription on app unmount
- Resolves issue where local relays disconnect after idle period in flight mode

src/App.tsx

@@ -118,6 +118,22 @@ function App() {
       console.log('Created relay group with', RELAYS.length, 'relays (including local)')
       console.log('Relay URLs:', RELAYS)
       
+      // Keep local relay connections alive indefinitely by creating a persistent subscription
+      // This prevents disconnection in flight mode when no other subscriptions are active
+      const localRelays = RELAYS.filter(url => url.includes('localhost') || url.includes('127.0.0.1'))
+      if (localRelays.length > 0) {
+        // Create a minimal subscription that never completes to keep connections alive
+        const keepAliveSub = pool.subscription(localRelays, { kinds: [0], limit: 0 }).subscribe({
+          next: () => {}, // No-op, we don't care about events
+          error: (err) => console.warn('Keep-alive subscription error:', err)
+        })
+        console.log('🔗 Created keep-alive subscription for', localRelays.length, 'local relay(s)')
+        
+        // Store subscription for cleanup
+        // eslint-disable-next-line @typescript-eslint/no-explicit-any
+        ;(pool as any)._keepAliveSubscription = keepAliveSub
+      }
+      
       // Attach address/replaceable loaders so ProfileModel can fetch profiles
       const addressLoader = createAddressLoader(pool, {
         eventStore: store,
@@ -134,6 +150,12 @@ function App() {
       return () => {
         accountsSub.unsubscribe()
         activeSub.unsubscribe()
+        // Clean up keep-alive subscription if it exists
+        // eslint-disable-next-line @typescript-eslint/no-explicit-any
+        if ((pool as any)._keepAliveSubscription) {
+          // eslint-disable-next-line @typescript-eslint/no-explicit-any
+          (pool as any)._keepAliveSubscription.unsubscribe()
+        }
       }
     }