refactor: remove custom font-weight scss and update class usages

Delete the standalone font-weight.scss utility file, remove its import from the main scss index, and update all existing references to the custom font-{weight} classes to use either built-in semantic font utilities or inline functional font weight classes matching the project's utility-first styling pattern.

src/static/scss/font-weight.scss

@@ -1,28 +0,0 @@
-// 字体-weight
-.font-bold {
-  font-weight: bold;
-}
-
-.font-400 {
-  font-weight: 400;
-}
-
-.font-500 {
-  font-weight: 500;
-}
-
-.font-600 {
-  font-weight: 600;
-}
-
-.font-700 {
-  font-weight: 700;
-}
-
-.font-800 {
-  font-weight: 800;
-}
-
-.font-900 {
-  font-weight: 900;
-}

src/static/scss/index.scss

@@ -2,7 +2,6 @@
 @import "./border.scss";
 @import "./display.scss";
 @import "./flex.scss";
-@import "./font-weight.scss";
 @import "./height.scss";
 @import "./font-size.scss";
 @import "./font-family.scss";