chore(nests): mv cli/hang-interop → nestsClient/tests/hang-interop

Per maintainer request: the Rust sidecar workspace lives
under the module that owns it, parallel to the upcoming
nestsClient-browser-interop/ harness. The cargo workspace,
Gradle wiring, gitignore, CI YAML, plan docs, and harness
kdoc are all updated. cargo build --release still compiles;
HangInteropTest.amethyst_speaker_to_hang_listener_stereo_440_660
green at the new path.

Note: the live Phase 4 browser-harness agent (worktree
agent-a97a6be483ecee618) was branched from before this move
and references `cli/hang-interop` in its plan-doc imports.
It will need to rebase onto this commit before it pushes;
no code-level conflicts since the agent works exclusively
in nestsClient-browser-interop/ + a new
BrowserInteropTest.kt.

https://claude.ai/code/session_01ERJPUYfdLPwZ99pr5EcEcV

nestsClient/src/jvmTest/kotlin/com/vitorpamplona/nestsclient/interop/native/NativeMoqRelayHarness.kt

@@ -36,7 +36,7 @@ import kotlin.concurrent.withLock
  * binary paths for the cross-stack interop harness.
  *
  *   - `moq-relay` is `cargo install`ed at the version pinned in
- *     `cli/hang-interop/REV` and cached under
+ *     `nestsClient/tests/hang-interop/REV` and cached under
  *     `~/.cache/amethyst-nests-interop/hang-interop-cargo/bin/`.
  *   - TLS: `--tls-generate localhost` so the relay self-signs at
  *     startup. Kotlin clients use the existing
@@ -95,7 +95,7 @@ class NativeMoqRelayHarness private constructor(
 
         /**
          * `interopBuildHangSidecars` writes this. Points to
-         * `cli/hang-interop/target/release` where the (Phase-1
+         * `nestsClient/tests/hang-interop/target/release` where the (Phase-1
          * stub) sidecar binaries live.
          */
         const val SIDECARS_DIR_PROPERTY = "nestsHangInteropSidecarsDir"