style(design-system): normalize font-weight literals (400/500/600/700) to tokens

Mechanical, value-preserving: font-weight: 400/500/600/700 -> var(--font-weight-normal/medium/semibold/bold, <same value>) across src/app.
Note: cart.component.scss now sits ~771 bytes over its per-file budget
in angular.json due to longer var() strings; non-fatal build warning,
noted in docs/UI-DESIGN-REVIEW.md as a follow-up (either bump the
component style budget slightly or accept the warning).

src/app/features/website/user-experience/compare/components/compare-table.component.scss

@@ -26,7 +26,7 @@
 
 .compare-product-title {
   font-size: var(--font-size-md, 0.9375rem);
-  font-weight: 700;
+  font-weight: var(--font-weight-bold, 700);
   line-height: 1.3;
 }
 

src/app/features/website/user-experience/compare/containers/compare-page.component.scss

@@ -33,7 +33,7 @@
   gap: 8px;
   align-items: center;
   color: var(--text-primary);
-  font-weight: 600;
+  font-weight: var(--font-weight-semibold, 600);
 }
 
 .compare-products-list {
@@ -55,7 +55,7 @@
 .compare-product-chip a {
   color: var(--text-primary);
   text-decoration: none;
-  font-weight: 600;
+  font-weight: var(--font-weight-semibold, 600);
 }
 
 .compare-product-chip button {

src/app/features/website/user-experience/components/floating-notifications/floating-notifications.component.scss

@@ -24,7 +24,7 @@
 .floating-note p {
   margin: 0;
   color: var(--text-primary);
-  font-weight: 600;
+  font-weight: var(--font-weight-semibold, 600);
   line-height: 1.3;
 }