Publish releases from macOS so iOS targets resolve

[kdroidFilter]

Problem

dev.nucleusframework:composewebview:1.0.0 cannot be resolved by any KMP project with Apple targets (#51):

> Could not find composewebview:webview-compose-iosarm64:unspecified.

The publish job ran on ubuntu-latest, where iosArm64 / iosSimulatorArm64 are disabled. Kotlin still emits their variants in the root Gradle module metadata, but with Gradle's default project coordinates instead of the publication's. The shipped composewebview-1.0.0.module therefore contains:

"available-at": {
  "group": "composewebview",
  "module": "webview-compose-iosarm64",
  "version": "unspecified"
}

while every other target correctly points at dev.nucleusframework:composewebview-*:1.0.0. The iOS klibs were never published at all.

Fix

• publish now runs on macos-15, reusing the Xcode selection from the iOS jobs in pr-build-check.yml. Natives keep coming from the build-natives matrix artifacts, so nothing else about the job changes.
• New :webview-compose:verifyPublicationCoordinates reads the generated root module.json and fails if any available-at entry falls outside the group/version being published. It is wired as a dependency of every AbstractPublishToMaven task, so a wrong publish host can never ship a dangling module again.

Verification

1. Guard rejects the broken release — fed the real composewebview-1.0.0.module from Maven Central:

> Root module metadata points at modules outside this publication:
    iosArm64ApiElements-published -> composewebview:webview-compose-iosarm64:unspecified
    ... (8 entries)
  Expected dev.nucleusframework:*:1.0.0.

and passes on a macOS publish: Publication coordinates OK: 20 variants under dev.nucleusframework:*:0.1.0-SNAPSHOT.

2. Consumer project, issue reproduced then fixed. A scratch KMP module with iosArm64 + iosSimulatorArm64 calling rememberWebViewState / WebView from commonMain:

dependency	:shared:compileKotlinIosArm64
composewebview:1.0.0 (Maven Central)	❌ Could not find composewebview:webview-compose-iosarm64:unspecified
composewebview:1.0.1-e2e (published from macOS)	✅

With the fixed publication, :shared:dependencies --configuration iosArm64CInterop — the exact configuration from the issue — resolves to dev.nucleusframework:composewebview-iosarm64:1.0.1-e2e, and :shared:linkDebugFrameworkIosSimulatorArm64 links shared.framework successfully.

3. No regression — ./gradlew :e2e-desktop:run on macOS: SUITE_FINISHED passed=true (full visual suite, real WKWebView).

Closes #51