Fixed grid, custom shapes using line tool

[Finyti]

Story

Hi!
I would like to introduce a few must-have features, that I think edgeless mode should support.

So, for me, the main use case for visual note-taking apps is studying, specifically taking notes and using all the features of the whiteboard. Despite that, I always wanted to have the ability to organize and log my everyday activity in the same environment where I do actual work. For me, Affine is the first tool I found that could unite both of these use-cases in one whole. I was really excited to make a switch, but while field-testing the app, I found out that in practise it is really inconvenient to study STEM subjects. Just for example, if I need to construct a shape that is not provided in a toolbox, I have no tools to do so. If I want to draw a graph, I can't really make a curve, nor have a meaningful way to define a unit on the graph. There is no easy way to create shapes with uniform proportions, because the grid changes with the canvas zoom, and the grid itself can't be adjusted.

So here are my feature ideas:

Description

1. Ability to make a fixed grid of chosen size.
   Such a grid, while snapping to the grid is enabled, would allow for easy creation of different shapes of uniform proportions, with easy aligning. Additionally, a fixed grid would allow for reliable point of reference for size of drawings or handwriting.
   Example of a grid in action (Excalidraw):
   

2. An editable line tool.
   For now, lines in Affine are created using curve tool. Sadly, it cannot be used for shape construction, nor you can specify a path for it. Really it is just a connector tool. But look at what you could do with a line tool which path can be edited (Excalidraw):

Curve tool could be either enriched with such functionality, or split into two separate tools. One would maintain arrow/linkage functionality, while a new tool could be added into shape tools list.

Use case

The use case for these features would be practically universal, because they are improvements of the Affine whiteboard that would enable more use cases for the Affine to exist, more ways to express creativity in already existing use cases and make interaction with a whiteboard much more pleasant when it comes to aligning and resizing things