Install gum prior to the preflight guard (#684)

* Use `read` instead of `gum` in the preflight guard

* Revert "Use `read` instead of `gum` in the preflight guard"

This reverts commit 759dbb70454dccc27b78b198bf077e076750fefc.

* Install `gum`, if required, at the beginning of `install.sh`

* `gum` is already installed by the `presentation.sh` stage

* Use existing structure

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Co-authored-by: David Heinemeier Hansson <david@hey.com>

install/preflight/gum.sh

@@ -0,0 +1,3 @@
+#!/bin/bash
+
+yay -S --noconfirm --needed gum

install/preflight/presentation.sh

@@ -1,3 +0,0 @@
-#!/bin/bash
-
-yay -S --noconfirm --needed gum python-terminaltexteffects

install/preflight/tte.sh

@@ -0,0 +1,3 @@
+#!/bin/bash
+
+yay -S --noconfirm --needed python-terminaltexteffects