v1.4.1: Test Relay aware of Full mode + ship missing mipsel artifact

Patch release covering:

- #160 (deniz_us): Test Relay returned Google datacenter IPs even in
  Full Tunnel mode, because test_cmd::run unconditionally used
  fronter.relay() (apps_script path) regardless of configured mode.
  The user's tunnel-node was actually working — whatismyipaddress.com
  in their browser showed the correct VPS IP — but Test Relay
  contradicted it. Now Test Relay refuses cleanly in Full mode with
  a clear message and points users at the right verification path.
  A real Full-mode test through the tunnel mux is enhancement-tracked.

- mhrv-rs-openwrt-mipsel-softfloat artifact lands natively (commit
  febeeca). v1.4.0 had a build break on the 32-bit MIPS target due to
  PR #153's std::sync::atomic::AtomicU64 import — switched to
  portable_atomic::AtomicU64 which is already the project's
  convention for that reason. The artifact was hot-published to the
  v1.4.0 release page via workflow_dispatch yesterday; v1.4.1 ships
  it the normal way.

91 tests pass.

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

Cargo.lock

@@ -2186,7 +2186,7 @@ dependencies = [
 
 [[package]]
 name = "mhrv-rs"
-version = "1.4.0"
+version = "1.4.1"
 dependencies = [
  "base64 0.22.1",
  "bytes",