refactor(build): consolidate architecture guard tasks into reusable custom Gradle scripts

Replaced task implementations for `ForbiddenAuthorizationHeaderTask`, `FeatureIsolationTask`, and `BundleBudgetTask` with dedicated buildSrc scripts for improved clarity and maintainability. Updated task registrations accordingly in `build.gradle.kts`.

buildSrc/src/main/kotlin/at.mocode.architecture-guards.gradle.kts

@@ -0,0 +1,19 @@
+import at.mocode.gradle.ForbiddenAuthorizationHeaderTask
+import at.mocode.gradle.FeatureIsolationTask
+
+tasks.register<ForbiddenAuthorizationHeaderTask>("archGuardForbiddenAuthorizationHeader") {
+    group = "verification"
+    description = "Fail build if code sets Authorization header manually."
+}
+
+tasks.register<FeatureIsolationTask>("archGuardNoFeatureToFeatureDeps") {
+    group = "verification"
+    description = "Fail build if a :frontend:features:* module depends on another :frontend:features:* module"
+}
+
+tasks.register("archGuards") {
+    group = "verification"
+    description = "Run all architecture guard checks"
+    dependsOn("archGuardForbiddenAuthorizationHeader")
+    dependsOn("archGuardNoFeatureToFeatureDeps")
+}

buildSrc/src/main/kotlin/at.mocode.bundle-budget.gradle.kts

@@ -0,0 +1,6 @@
+import at.mocode.gradle.BundleBudgetTask
+
+tasks.register<BundleBudgetTask>("checkBundleBudget") {
+    group = "verification"
+    description = "Checks JS bundle sizes of frontend shells against configured budgets"
+}