feat(wm): add theme socket message

This commit adds a new SocketMessage::Theme which allows for themes to
be set programmatically. This change has also been plumbed through to
komorebi-bar so that the bar theme will also update after komorebi
processes the message and passes it on to subscribers.

A new theme_manager module has been introduced to add notification-based
handling of theme changes, both from the static config file being
updated and from SocketMessage::Theme being received.

schema.bar.json

@@ -1428,6 +1428,7 @@
               ]
             },
             "name": {
+              "description": "Name of the Catppuccin theme (theme previews: https://github.com/catppuccin/catppuccin)",
               "type": "string",
               "enum": [
                 "Frappe",
@@ -1474,6 +1475,7 @@
               ]
             },
             "name": {
+              "description": "Name of the Base16 theme (theme previews: https://tinted-theming.github.io/base16-gallery)",
               "type": "string",
               "enum": [
                 "3024",