Fixed dark and light themes, ui.theme auto/dark/light

Colors no longer come from the terminal's palette, whose color 0 many
color themes set to a grey that is not their background. A theme sets
tview's default styles and the color names used in texts, all chosen from
entries 16-255 of the 256-color table so terminals without 24-bit color
show them exactly. "auto" picks light or dark from the background color
the terminal reports. Settable in the Config view, applied at the next
start (widgets copy their colors when created). Replaces using the
terminal's own background and text colors.

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

internal/ui/help.go

@@ -66,12 +66,12 @@ var helpSections = []helpSection{
 		{"t", "retry a failed download (history)"},
 		{"r", "refresh now"},
 	}},
-	{title: "Config (F6)", note: "Edit the settings of the config file: service addresses and API keys, add-form defaults, refresh interval, posters, notifications.", items: []helpItem{
+	{title: "Config (F6)", note: "Edit the settings of the config file: service addresses and API keys, add-form defaults, refresh interval, posters, theme, notifications.", items: []helpItem{
 		{"↑↓", "move through all fields, one below the other, in the sections Radarr, Sonarr, SABnzbd and Interface; ↓ after the last field reaches Save and Revert"},
 		{"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; Revert discards edits"},
+		{"Save, Revert", "(at the bottom) Save writes the file and applies everything at once (the theme at the next start); Revert discards edits"},
 	}},
 	{title: "Log (F7)", note: "Popups fade away by themselves; everything they said is kept here.", items: []helpItem{
 		{"↑↓, PgUp, PgDn", "scroll"},