perf(mobile): lower StopClient join timeout from 3s to 1s and log slow shutdown (#20)

When the user taps Disconnect, `GooseRelayVpnService.stopVpn()` waits up to **5 seconds** (`stopThread.join(5000L)`) for Go's `StopClient()` to return. Inside `StopClient()`, after the carrier `cancel()` and SOCKS listener close, it waits *another* up to **3 seconds** on `<-clientDone`. The inner 3s timeout is redundant with the outer 5s join.

On a healthy disconnect where the carrier shuts down in <200ms (the common case), the user still sees ~3s of "DISCONNECTING" + 500ms fade ≈ **3.5s**, where the inner 3s timeout is the sole contributor — the outer 5s never kicks in.

**Change:** Lower the inner `<-clientDone` wait from `3s → 1s`. If the carrier takes longer than 1s, log it and return — the outer 5s join still caps total disconnect at a sane value. Healthy disconnect drops from ~3.5s → ~1.5s with no behavioral regression.

The new `[client] carrier shutdown exceeded 1s` log line surfaces slow shutdowns for debugging without changing `StopClient`'s gomobile API surface (which would ripple to Kotlin callers).

## Files changed

- `mobile/mobile.go` — single block replacement (+9/-1)

## CI gates to watch

- `go vet` (Linux — `syscall.Dup` resolves; the Windows-only vet error in `dupFd` is pre-existing, unrelated)
- AAR build (`bash ./android/build_go_mobile.sh`)
- `./gradlew :app:assembleDebug`

Author: Hidden-Node

mobile/mobile.go

@@ -239,7 +239,15 @@ func StopClient() {
 	if done != nil {
 		select {
 		case <-done:
-		case <-time.After(3 * time.Second):
+		case <-time.After(1 * time.Second):
+			// The carrier shutdown took longer than 1s. The outer
+			// Android caller (GooseRelayVpnService.stopVpn) caps total
+			// disconnect with a 5s outer join, so we return promptly
+			// here and let the outer caller decide whether to log a
+			// "stop timed out" message. StopTun/StopTunBridge below are
+			// idempotent and safe to call even if the carrier is still
+			// winding down.
+			log.Printf("[client] carrier shutdown exceeded 1s, proceeding with TUN teardown")
 		}
 	}