implement-flet-extension

Implement a Flet extension around an external Flutter package using existing `flet_*` packages as implementation templates. ## Inputs - Control/service name and Python package name (`flet_<extension>`). - Target pub.dev package and intended version/range. - API surface to expose in Python (properties, methods, events, types/enums). ## Third-party Dependency Gate 1. Confirm package health: maintenance activity, null-safety, platform support, and open issue risk. 2. Confirm license is compatible with Flet distribution. 3. Select a conservative version strategy: - Pin exact version when behavior stability is critical. - Use bounded ranges when required by ecosystem constraints. 4. Record key constraints and reasons in PR notes/commit message. ## Control/Service Classification - Classify wrapped functionality before implementation: 1. `LayoutControl` for visual controls that participate in page/layout positioning. 2. Base `Control` for simple visual controls that do not require page positioning or define their own positioning rules/props (for example `Draggable`, `Divider`, `MenuBar`, `NavigationRail`). 3. Non-visual Service when functionality is not a renderable UI control. - Inspect the wrapped Flutter package API to determine whether it includes non-visual/service functionality. - For service patterns, follow existing extension examples: `sdk/python/packages/flet-audio`, `sdk/python/packages/flet-flashlight`, `sdk/python/packages/flet-secure-storage`. ## API Mapping Rul...