chore(frontend): upgrade Bootswatch and Bootstrap SCSS to v5.3.3

- Upgraded Bootswatch SCSS source files across all 25 themes (dev/scss/bootswatch/) to v5.3.3
- Upgraded Bootstrap SCSS source files (dev/scss/bootstrap/) to v5.3.3 to match static/js/bootstrap.bundle.min.js
- Updated dev/scss/bootstrap-overrides.scss to import bootstrap/variables-dark
- Verified error-free LibSass compilation for all 26 themes (25 Bootswatch + bootstrap-orj)
- Recompiled static/css/wvc-main.min.css

dev/scss/bootstrap/forms/_input-group.scss

@@ -121,7 +121,7 @@
   }
 
   > :not(:first-child):not(.dropdown-menu)#{$validation-messages} {
-    margin-left: -$input-border-width;
+    margin-left: calc(#{$input-border-width} * -1); // stylelint-disable-line function-disallowed-list
     @include border-start-radius(0);
   }