Show square brackets in the neoirc-cli message window as written (closes #233)

The message window has colour tags on, so tview read square-bracket
text in nicks, channel names, reasons, topics and message text as
tags. It dropped that text or changed the colour of the rest of the
line.

A new escape in internal/cli/ui.go writes each "[" as "[[:]", and
app.go applies it to every part of a line that comes from the user or
the server. tview.Escape is not used: it misses bracket pairs holding
symbols such as "|", and tags with a URL.

Lines for other server commands now show the command, such as
"[MODE]", which tview had read as a tag.

Model: opus-5-5

internal/cli/ui.go

@@ -235,6 +235,16 @@ func (ui *UI) initMessages() {
 	ui.messages.SetBorder(false)
 }
 
+// escape returns text so that the message window shows it exactly
+// as written. It writes each "[" as "[[:]": a "[" followed by
+// another "[" never starts a tag, and the tag "[:]" changes
+// nothing. tview.Escape is not enough: it does not escape a bracket
+// pair holding a symbol such as "|" or "^", and nothing it adds
+// stops a tag with a URL, such as "[:::y|z]".
+func escape(text string) string {
+	return strings.ReplaceAll(text, "[", "[[:]")
+}
+
 func (ui *UI) initStatusBar() {
 	// Colour tags stay off. With them on, tview reads text in
 	// square brackets, such as "[connected]" or part of a nick,