Parent

Part of #1402. Depends on Phase 4.

Goal

Introduce a MonitoringState machine (Running / Paused / Stopped) inside the root-level core crate and stop tying the app process lifecycle to the main window's close event.

Workspace Context

core::monitoring lives at core/src/monitoring/ in the workspace core crate; lifecycle wiring lives at src-tauri/src/app/lifecycle.rs and depends on the core crate.

Scope

• Add core::monitoring::MonitoringState with explicit transitions in core/src/monitoring/.
• Move start/stop wiring into app::lifecycle (src-tauri/src/app/lifecycle.rs).
• on_window_event(CloseRequested) no longer calls WorkersState::terminate_all() and no longer calls app.exit(0). It hides the window instead.
• An explicit Quit action (initially behind a debug flag or hidden setting) stops Core cleanly: state machine → Stopped, persistence flush, then app.exit(0).
• Existing release behavior (closing the window quits the app) is preserved for end-users in this phase by gating the new behavior. The user-facing change ships with feat: add background monitoring mode with system tray support #1275.

Out of Scope

• Tray UI (Phase 6).
• "Close to tray" setting / first-run dialog (owned by feat: add background monitoring mode with system tray support #1275).

Definition of Done

• With the debug flag enabled, the app keeps running with no visible window; collector and persistence continue.
• Quit exits cleanly with no orphaned tasks and DB writes flushed.
• MonitoringState transitions have unit tests covering all valid and invalid transitions, runnable via cargo test -p <core-crate> without a Tauri runtime.
• Default release behavior is unchanged for users until feat: add background monitoring mode with system tray support #1275 lands.

Notes

This phase is intentionally invisible to end users. The visible UX changes (tray menu, "close to tray" setting, first-run dialog) are owned by #1275.