v1.2.10: proxy Stop actually stops now (fix issue #99)

Single-focus release. The Stop button in the UI previously only
stopped new connections from being accepted — in-flight clients kept
running on the old DomainFronter, which meant:

- Pages kept loading after Stop (users thought they'd stopped)
- Auth-key changes didn't take effect for domains with a live
  keep-alive to the proxy
- Apps Script quota could still be consumed post-Stop

Fix (7338e76): wrap per-client spawns in a tokio::task::JoinSet
inside each accept loop. On shutdown, aborting the accept task drops
the JoinSet, which aborts every in-flight client. Sockets close,
the old fronter's TLS pool drops, and a subsequent Start builds a
clean new state.

Finding 1 of #99 (quota-exceeded → "timeout" instead of the real
502 body) is a separate pool-staleness issue and is NOT addressed
in this release.

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 = 129
-        versionName = "1.2.9"
+        versionCode = 130
+        versionName = "1.2.10"
 
         // Ship all four mainstream Android ABIs:
         //   - arm64-v8a      — 95%+ of real-world Android phones since 2019