Parent

Part of #1402. Depends on the new Phase 1 (workspace setup).

Goal

Add core::event_bus::EventBus (tokio::sync::broadcast<MetricsSnapshot>) inside the root-level core crate and route the existing real-time monitor event through it. Frontend behavior unchanged.

Workspace Context

After the new Phase 1, core/ is a separate crate at the repo root. Items under core::* in this issue refer to modules inside that crate (core/src/...). src-tauri/ continues to host the Tauri app and depends on the core crate via path.

Scope

• Implement core::event_bus::EventBus and a MetricsSnapshot payload type in core/src/event_bus.rs (with MetricsSnapshot in core/src/models/).
• Modify workers::system_monitor::SystemMonitorController (still under src-tauri/src/workers/) to publish to the EventBus via the core crate API instead of calling app.handle() directly for emit.
• Add app::adapters::window::WindowAdapter under src-tauri/src/app/adapters/window.rs that subscribes to the EventBus and emits the existing HardwareMonitorUpdate Tauri event.
• The HardwareMonitorUpdate wire format stays unchanged this phase.

Out of Scope

• Moving the collector under core/ (Phase 3).
• Replacing HardwareMonitorUpdate with a redesigned payload (deferred).

Definition of Done

• Frontend dashboard updates in real time, indistinguishably from before.
• Inside the collector loop, there is no direct call to tauri::Emitter::emit or AppHandle::emit.
• A unit test under core/ exercises EventBus fan-out to multiple subscribers without a Tauri runtime — i.e. cargo test -p <core-crate> passes with no Tauri in the dependency graph.