Refactor FontManager theme loading and add default theme getter

lib/utils/font_manager.lua

@@ -36,6 +36,7 @@ end
 --- A singleton to handle fonts
 --- @class FontManager
 --- @field private _themes table
+--- @field defaultTheme string?
 local FontManager = {
     _themes = {}
 }
@@ -54,14 +55,14 @@ function FontManager.newFont(name, size)
 end
 
 --- @param name string
---- @return TextTheme?
+--- @return FontManager
 function FontManager:loadTheme(name)
     self._themes[name] = theme.new(
         function(size)
             return self.newFont(name, size)
         end
     )
-    return self._themes[name]
+    return self
 end
 
 --- @param name string
@@ -70,14 +71,20 @@ function FontManager:getTheme(name)
     return self._themes[name]
 end
 
+--- @return TextTheme
+function FontManager:getDefaultTheme()
+    return self._themes[self.defaultTheme]
+end
+
 --- initial setup
 --- @param defaultFontName string
 function FontManager:load(defaultFontName)
-    local t = self:loadTheme(defaultFontName)
+    local t = self:loadTheme(defaultFontName):getTheme(defaultFontName)
     if not t then
         print("[FontManager]: default font " .. defaultFontName .. " is missing")
         return self
     end
+    self.defaultTheme = defaultFontName
 
     local f = t:getVariant("medium")
     love.graphics.setFont(f)