Get new app ready for first user tests

[lucasmerlin]

• some brush should be selected by default
• on finite boards, a layer should be selected by default
• add some feedback to board creation if there was an error
• profile form validaiton
• create canvas
• delete layer
• fix loading spinner showing if list is empty
• maybe optional: implement pressure sensitivity for other brush values like opacity etc and add angle sensor to affect rotation
• Fix select tool
• Fix layers getting darker on each render
• Fix board preview being updated on each stroke
• distortion when the canvas is rotated
• eraser
• Get keyboard working again on android
• Get keyboard working again on ios
• fix gamma: Do all blending in linear (non-srgb) space. Switch egui wgpu to render to srgb texture (or render to a temp texture). Also check whether the eraser now looks correct.
  I gave up on this: Gamma correct blending #49
• fix brush preview being offset
• Store visibility / opacity / name / clip layer settings
• brush opacity
• Remember the last used brush
• Keep color when switching brushes
• Fix brush not working (normal brush seems to be stuck as eraser)
• automatically select canvas after creation and deselect select tool
• Switch to brush tool when changing color
• Show root list when infinite layer is selected
• Object sorting
• highlight the currently selected canvas in some way
• Connection lost error message
• Prevent creation of 0x0 canvases
• Render tiles at lower zoom levels
• Make renderer respect distribution
• Switch back to brush after picking color (?)
• Add some way to use the color picker on touch
• fix clipping: render the clipped layers directly in the shader of the clipping layer and apply some sort of limit of how many layers can be clipped to one layer?
• color history
• some way to filter and delete brush presets
• add / improve default brushes
• Fix brush list not loading sometimes