Refactor(2D): Modularize Floor2D, add Move tool, context menu actions, and UX improvements

[Abdo-Eid]

Summary

• Refactors and modularizes the 2D floor implementation. Replaces the monolithic src/js/2d/floor2d.js with modular files to improve maintainability and performance.
• Adds new features: Move tool (Alt to drag vertices or drag canvas), extended context menu actions (Delete Line, Clear Canvas), and improved hints UI.
• Fixes canvas resize issues when toggling between 2D/3D and improves panning stability and grid behavior.

Testing checklist (please run before merging)

• Start dev server and open the app in 2D mode
• Create and edit lines/shapes using drawing tools
• Use the Move tool: hold Alt and drag vertices — ensure vertices move and shapes update
• Right-click on canvas to open context menu: verify 'Delete Line' and 'Clear Canvas' actions work
• Toggle between 2D and 3D modes — verify canvas resizes properly and no JS errors appear
• Load a DXF file (use simple_test.dxf) — verify entities render and behave correctly
• Confirm grid and panning behavior for large canvases (infinite grid behavior)

Notes for reviewers

• undo code of amer @iamAmer is removed for now, I'm working on undo redo feature that uses command pattern, but still thinking of a good structure.
  @pcolt @mfranzon