v1.6.1: Android VPN session lifecycle reliability (#187)

Five small but real Android-only fixes:

1. Connect/Disconnect button gated on VpnState.isRunning state-flow
   with 12s backstop, replacing the fixed 2s transitionCooldown
   timer. Closes the race where a tap-after-Stop hit "Address already
   in use" because the previous teardown's listener-socket release
   wasn't done.

2. Tun2proxy.stop() wrapped in 2s join() — if the native call hangs,
   bounded teardown still releases the listener port instead of
   holding the teardown thread.

3. fd-leak fixed between parcelFd.detachFd() and Thread.start(): an
   OOM-thrown Thread.start used to orphan the detached fd. Now
   adopted into a fresh ParcelFileDescriptor purely so we can close()
   it.

4. Misleading teardown doc-comment rewritten — the "step 2 closes
   the TUN fd to force EBADF on read" claim has been factually
   wrong since detachFd landed.

5. Recursive crash trap: Log.e in MhrvApp's uncaught handler now
   wrapped in try/catch so a logd failure during exception logging
   falls through to the previous handler with the real exception.

No Rust changes; 98 lib + 22 tunnel-node tests still pass.

Local Android build verified, APK installed on mhrv_test emulator,
launches cleanly with v1.6.1 in title.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

android/app/build.gradle.kts

@@ -14,8 +14,8 @@ android {
         applicationId = "com.therealaleph.mhrv"
         minSdk = 24 // Android 7.0 — covers 99%+ of live devices.
         targetSdk = 34
-        versionCode = 139
-        versionName = "1.6.0"
+        versionCode = 140
+        versionName = "1.6.1"
 
         // Ship all four mainstream Android ABIs:
         //   - arm64-v8a      — 95%+ of real-world Android phones since 2019