fix: clear screen after setting shell

examples/demo.tape

@@ -50,6 +50,7 @@ Output examples/demo.gif
 
 Require echo
 
+Set Shell "bash"
 Set FontSize 32
 Set Width 1200
 Set Height 600

shell.go

@@ -14,32 +14,39 @@ const (
 type Shell struct {
 	Prompt  string
 	Command string
+	Clear   string
 }
 
 // Shells contains a mapping from shell names to their Shell struct.
 var Shells = map[string]Shell{
 	bash: {
 		Prompt:  "\\[\\e[38;2;90;86;224m\\]> \\[\\e[0m\\]",
 		Command: ` PS1="%s" bash --login --norc --noprofile +o history; clear;`,
+		Clear:   "clear",
 	},
 	zsh: {
 		Prompt:  `%F{#5B56E0}> %F{reset_color}`,
 		Command: ` PROMPT="%s" zsh --login --histnostore --no-rcs; clear;`,
+		Clear:   "clear",
 	},
 	fish: {
 		Prompt:  `function fish_prompt; echo -e "$(set_color 5B56E0)> $(set_color normal)"; end`,
 		Command: ` fish --login --no-config --private -C 'function fish_greeting; end' -C '%s'; clear;`,
+		Clear:   "clear",
 	},
 	powershell: {
 		Prompt:  `Set-PSReadLineOption -HistorySaveStyle SaveNothing; Function prompt { Write-Host -ForegroundColor Blue -NoNewLine '>'; return ' ' }`,
 		Command: ` clear; powershell -Login -NoLogo -NoExit -NoProfile -Command %q`,
+		Clear:   "clear",
 	},
 	pwsh: {
 		Prompt:  `Set-PSReadLineOption -HistorySaveStyle SaveNothing; Function prompt { Write-Host -ForegroundColor Blue -NoNewLine '>'; return ' ' }`,
 		Command: ` clear; pwsh -Login -NoLogo -NoExit -NoProfile -Command %q`,
+		Clear:   "clear",
 	},
 	cmdexe: {
 		Prompt:  "$g",
 		Command: ` cls && set prompt=%s && cls`,
+		Clear:   "cls",
 	},
 }

vhs.go

@@ -133,6 +133,10 @@ func (vhs *VHS) Setup() {
 		MustInput(shellCommand).
 		MustType(input.Enter)
 
+	vhs.Page.MustElement("textarea").
+		MustInput(vhs.Options.Shell.Clear).
+		MustType(input.Enter)
+
 	// Apply options to the terminal
 	// By this point the setting commands have been executed, so the `opts` struct is up to date.
 	vhs.Page.MustEval(fmt.Sprintf("() => { term.options = { fontSize: %d, fontFamily: '%s', letterSpacing: %f, lineHeight: %f, theme: %s } }",