fix: add --cursor-blink flag to disable terminal cursor blink

[fuleinist]

On macOS Kitty the blinking cursor triggers constant redraws (~500ms), making text selection and link hover nearly impossible.

This adds a --cursor-blink flag (default: true) so affected users can disable blinking with:

sbb-tui --cursor-blink=false

Fixes #27

[Necrom4]

Thanks for the PR!
Unfortunately it doesn't work, although the cursor is static when opening the TUI, it starts blinking again as soon as someone presses a key.

I recommend you go with a solution like this one:

# ui/model.go

# in the m.inputs range of NewModel
t.Cursor.Style = m.styles.active
+ t.Cursor.SetMode(cursor.CursorStatic) # don't forget to import `cursor` at the top of the file too

# in Init()
func (m appModel) Init() tea.Cmd {
-	return tea.Batch(textinput.Blink, checkVersionCmd(m.currentVersion))
+	return checkVersionCmd(m.currentVersion)
}

Also concerning your last commit, please for the next modifications format the model.go file correctly (misaligned definitions) and don't use double negatives ("DisableCursorBlink").

Lastly I'd very much rather have the cursor blink option as a default (to "true") in the config file rather than as a flag, as it's an option people will always want ON and it'd be anoying to constantly pass the flag. Don't forget to document your changes in the "config" section of the README.md!