replace the editor menubar dropdown flow with a reusable context menu
component
merge sprite/entity placement into a single object tool
persist entities, and add undo
support for created sprites and entities

add responsive editor relayout for window resize
rework header with back/save, view mode buttons, and 2d view type selector
add clipped, scrollable assets and contextual tool panels
simplify tool button wiring and repeated layout logic
simplify 2d top-down editor internals and shared grid update hooks

fix wall Z bounds calculation and key index masking in input handling
preserve 2D view/cursor stability when map bounds update