v0.9.0-alpha — Phase 9 polish

Polish pass before Marketplace/v1.0: <x-admob::banner> Blade component (no Livewire dependency), per-format/per-slot frequency caps (+ AdShowThrottled event), platform-aware App Open test ad unit, bridge-failure logging + ADMOB_DEBUG tracing, and a package-agnostic config/slot story (no env-key convention). 64 tests green. See CHANGELOG for details.