[Feature Request] Support Batch Selection of Graphical Elements

Description

When using FeynGame to draw Feynman diagrams, it is currently not possible to select and operate on multiple graphical elements (such as lines, vertices, or labels) at the same time. This makes it inefficient to edit complex diagrams. Expected Behavior

It would be helpful to support the following features:

Box selection of multiple elements using the mouse

Multi-selection via `Shift` or `Ctrl` click

Batch operations on selected items (e.g., move, copy, delete, align)