Add BindingKind enum, migrate legacy mouse gesture bindings, and update UI

[multiplex55]

Motivation

• Introduce explicit binding types for mouse gesture bindings so gestures can represent different behaviors (execute, set query, set query+show, toggle launcher) instead of relying on string prefixes or the legacy use_query flag.
• Preserve backward compatibility by migrating schema v1 gesture files to a new schema v2 and map old use_query/action formats to the appropriate new BindingKind.
• Surface binding kinds in the UI so users can pick the intended binding type and only edit relevant fields.

Description

• Added BindingKind enum to src/mouse_gestures/db.rs with variants Execute, SetQuery, SetQueryAndShow, and ToggleLauncher, and set SCHEMA_VERSION to 2 with a LEGACY_SCHEMA_VERSION = 1 fallback.
• Extended BindingEntry with kind: BindingKind and added action_string(), display_target() and updated to_action() to emit the correct Action (e.g., query: prefix, launcher:show, launcher:toggle) depending on BindingKind.
• Implemented migration in load_gestures to accept legacy schema v1 JSON and map legacy LegacyBindingEntry (including use_query and launcher:toggle) to the new BindingKind and fields.
• Updated binding search and display logic to use display_target() so searches and labels reflect the effective binding target.
• Updated the binding editor in src/gui/mouse_gestures_dialog.rs to present a radio/segmented control for binding Type, show only the relevant fields per kind, and populate the editor when picking actions/queries from plugins or the app list.
• Tweaked launcher activation in src/gui/mod.rs to handle launcher:show actions that carry a query in args and ensure focus behavior is applied correctly when those actions come from gestures.
• Added/updated tests and test data to reflect the new BindingKind usage and migration behavior in tests/mouse_gestures_db.rs, and updated references in tests/mouse_gestures_ui.rs and tests/mouse_gestures_service.rs.

Testing

• Ran cargo fmt to format code and ensure style consistency (succeeded).
• Attempted to run the test suite with cargo test including the updated mouse gesture tests, but the build failed during compilation due to a missing native system dependency required by alsa-sys (pkg-config/alsa.pc not found), so automated tests could not complete in this environment.
• New/modified tests added: gesture_db_migrates_legacy_schema (legacy v1 -> v2 migration), set_query_binding_avoids_execute_action (verifies SetQuery produces a query: action and does not invoke execute-action hooks), and updates to existing mouse gesture unit tests to include BindingKind in fixtures.

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Codex Task