Editing toolbar: select, copy/paste, and object manipulation

[BernardJen]

Summary

Introduce an editing toolbar that brings standard canvas editing: select, copy, paste, and basic object manipulation.

Motivation

As the canvas gains shapes, text, and imported paths, users need to manage individual objects — select them, duplicate them, and rearrange them — rather than treating the drawing as a single blob.

Toolbar / interactions

• Select — click to select an object; drag to box-select multiple.
• Copy / Paste — duplicate selected objects (keyboard shortcuts + toolbar buttons).
• Move selected objects.
• (Nice to have) delete, group/ungroup, z-order (bring forward / send back).
• Hosts tool toggles for drawing primitives and text (from the shapes/text issue).

Acceptance criteria

• A toolbar is visible with select / copy / paste actions.
• User can select single and multiple objects.
• Copy + paste duplicates the selection onto the canvas.
• Selected objects can be moved.
• Standard keyboard shortcuts work (Cmd/Ctrl+C, Cmd/Ctrl+V).

Notes

This is the interaction layer that the shapes/text and image-import features plug into.

[BernardJen]

Keystone issue. Introduces the shared object/scene model that #2, #3, #4, #5, #7, #8, and #9 all build on. Tracked in epic #10.