refactor(noctalia): move theme mode into the declarative config

The Settings UI stored `theme.mode` in ~/.local/state/noctalia/settings.toml, so it was not versioned. Pin it in the config baseline; the [location] sunrise/sunset schedule still drives light/dark.

home/linux/gui/base/noctalia/config/config.toml

@@ -24,6 +24,8 @@ directory = "~/Pictures/Screenshots"
 [theme]
 source = "builtin"
 builtin = "Catppuccin"
+# Follow the sunrise/sunset schedule from [location].
+mode = "auto"
 
 # Application theming is managed by catppuccin/nix, so Noctalia templates stay off.
 [theme.templates]