* Add input hints to fillet and chamfer tools
* Add hints to trimming tool
* Add hints to splitting tool
* Implement hints for extend tool
* Add hints to external geometry
* Add hints to Carbon Copy tool
* Hint updates to align with developer guidelines
* change "click to set" to "set" per PR comments
* Use enum (or declare one) to be type safe per PR comments
* For "trivial" one-step / one-state tools, refactor with direct hint return rather than using declarative / table pattern.
* Refactor hint tables initializers with C++20 features per PR feedback
- Use designated initializers (.state = , .hints = ) for clearer structure
- Add 'using enum Gui::InputHint::UserInput' to eliminate repetitive prefixes
- Applied to DrawSketchHandlerExtend and DrawSketchHandlerFillet
* Refactor Splitting tool hint implementation with direct return (trivial) pattern
* For fillet change "vertex" to "point" per PR feedback
* Change hint to "pick location on edge to split" per PR feedback
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