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

Mirrors the existing nestsClient/tests/hang-interop/ layout — all
T16 cross-stack interop test infrastructure (Rust sidecars + bun
browser harness) now lives under nestsClient/tests/.

Updates:
- nestsClient/build.gradle.kts: browserInteropDir path.
- PlaywrightDriver.kt + BrowserInteropTest.kt: kdoc comments.
- All plan docs in nestsClient/plans/ that referenced the old
  path.

Compiles clean post-move. No CI changes (those jobs are
intentionally not wired per 2026-05-07-cross-stack-interop-ci-gating.md;
when re-added they'll reference the new path).

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

@@ -138,7 +138,7 @@ class BrowserInteropTest {
      * `Container.Consumer`", but two constraints reshape this here:
      *
      *   1. `@moq/hang` 0.2.4 (the published version pinned in
-     *      `nestsClient-browser-interop/package.json`) does not export
+     *      `nestsClient/tests/browser-interop/package.json`) does not export
      *      the high-level `Container.Consumer` / `Format` API. Phase 4
      *      uses `Container.Legacy.Consumer` directly — same data path
      *      `@moq/watch` uses internally for `container.kind = "legacy"`.

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

@@ -52,7 +52,7 @@ internal object PlaywrightDriver {
     const val ENABLE_PROPERTY = "nestsBrowserInterop"
 
     /**
-     * Forwarded by Gradle: absolute path to `nestsClient-browser-interop/`.
+     * Forwarded by Gradle: absolute path to `nestsClient/tests/browser-interop/`.
      */
     const val HARNESS_DIR_PROPERTY = "nestsBrowserInteropHarnessDir"