Add dashboard gesture widgets, usage logging, and stats snapshot

[multiplex55]

Motivation

• Surface mouse-gesture information in the dashboard (cheat sheet, recent usage, health) and allow quick editing/toggling from the dashboard.
• Provide a dashboard-ready gesture data snapshot (DB + recent usage) so widgets render from a cached snapshot rather than performing IO in render paths.
• Add simple gesture statistics and unit test coverage for detecting unbound/duplicate/disabled gestures.

Description

• Added three dashboard widgets under src/dashboard/widgets/: gesture_cheat_sheet.rs (top-N gestures + primary binding + enable toggle + settings), gesture_recent.rs (recent gesture usage list + binding index), and gesture_health.rs (counts: zero bindings, duplicate tokens, disabled gestures + quick actions).
• Registered new widgets and their default/settings hooks in src/dashboard/widgets/mod.rs and added helper actions gesture_focus_action and gesture_toggle_action for invoking gesture dialog focus and toggle behavior.
• Extended dashboard snapshot with GestureSnapshot and wired DashboardDataCache::refresh_gestures to load mouse_gestures.json and a new usage log mouse_gestures_usage.json so widgets read from DashboardDataCache::snapshot() (src/dashboard/data_cache.rs).
• Added gesture usage logging support in src/mouse_gestures/usage.rs and recorded usage in the gesture runtime (src/mouse_gestures/service.rs).
• Introduced mouse_gestures::selection (serializable args for focus/toggle), mouse_gestures::stats (computes gesture stats), and updated GUI plumbing to watch gesture files and handle mg:dialog:focus and mg:toggle actions that open/focus the gesture dialog or toggle a gesture (src/gui/mod.rs, src/gui/mouse_gestures_dialog.rs).
• Tests/coverage: added a unit test for gesture stats in src/mouse_gestures/stats.rs and updated tests/dashboard_config.rs to assert the new widget registry entries exist.

Testing

• Added unit test gesture_stats_detects_unbound_and_duplicates in src/mouse_gestures/stats.rs and a registry assertion test in tests/dashboard_config.rs (these will run in CI).
• Attempted to run the gesture stats test locally with cargo test gesture_stats_detects_unbound_and_duplicates -- --nocapture, but the build failed due to a missing system library required by a dependency (alsa for alsa-sys), so local test execution was blocked by the environment; tests are expected to run in CI where system deps are present.

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Codex Task