fix(view): constrain cursor in insert mode (#93)

Problem: `constrain_cursor` only fired on `CursorMoved` and
`ModeChanged`, so arrow key navigation in insert mode could move
the cursor into the concealed ID prefix area.

Solution: add `CursorMovedI` to the autocmd event list. The
`constrain_cursor()` function is already mode-agnostic.

lua/canola/view.lua

@@ -552,7 +552,7 @@ M.initialize = function(bufnr)
       end
     end,
   })
-  vim.api.nvim_create_autocmd({ 'CursorMoved', 'ModeChanged' }, {
+  vim.api.nvim_create_autocmd({ 'CursorMoved', 'CursorMovedI', 'ModeChanged' }, {
     desc = 'Update canola preview window',
     group = 'Canola',
     buffer = bufnr,