Align backend composition API with edit_<object>() naming and role-based Haru helper classes

[Copilot]

The backend composition API used *_edit_methods() naming and generic helper class names, which diverged from the requested convention. This update aligns edit accessors to edit_<object>() and renames composed Haru objects to classes that explicitly describe what they manage.

• Backend interface naming

  • Renamed IDocraftRenderingBackend accessors from:
    • line_edit_methods(), shape_edit_methods(), text_edit_methods(), image_edit_methods(), page_edit_methods()
  • To:
    • edit_line(), edit_shape(), edit_text(), edit_image(), edit_page()
  • Kept getter semantics as const ...() const.

• Haru composed object naming

  • Replaced nested *EditMethods classes with role-specific classes:
    • LineHaruBackend, ShapeHaruBackend, TextHaruBackend, ImageHaruBackend, PageHaruBackend.
  • Updated construction/member wiring accordingly.

• Call site and contract alignment

  • Updated all usages across document context, mock backend, and Haru backend tests to the new accessor names.
  • Updated contributor docs that referenced the old *_edit_methods() pattern.

Example (new style):

class IDocraftRenderingBackend {
public:
    [[nodiscard]] virtual const std::shared_ptr<IDocraftTextRenderingBackend>& edit_text() const = 0;
};

class DocraftHaruBackend : public IDocraftRenderingBackend {
public:
    class TextHaruBackend;
    [[nodiscard]] const std::shared_ptr<IDocraftTextRenderingBackend>& edit_text() const override;
};

[sonarqubecloud]

Quality Gate failed

Failed conditions
32.2% Duplication on New Code (required ≤ 3%)

See analysis details on SonarQube Cloud