Switch the theme live

Widgets copy their colors when they are created, so they now get role
tokens (one unique RGB value per role) instead of colors, and a wrapper
around the tcell screen replaces the tokens with the current theme's
colors in SetContent. Changing the theme in the Config view swaps that
table; the next draw recolors everything. Poster colors that equal a
token are nudged off it.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_019reK4DUGYqDUjniWYJvwUW

internal/ui/help.go

@@ -71,7 +71,7 @@ var helpSections = []helpSection{
 		{"Tab", "jump between the fields and Save / Revert"},
 		{"Space", "toggle a checkbox; press a button"},
 		{"Test", "(button below the SABnzbd settings) checks the three services with the values typed in"},
-		{"Save, Revert", "(at the bottom) Save writes the file and applies everything at once (the theme at the next start); Revert discards edits"},
+		{"Save, Revert", "(at the bottom) Save writes the file and applies everything at once; Revert discards edits"},
 	}},
 	{title: "Log (F7)", note: "Popups fade away by themselves; everything they said is kept here.", items: []helpItem{
 		{"↑↓, PgUp, PgDn", "scroll"},