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/pages/legal/company-details/company-details.component.scss

@@ -15,14 +15,14 @@
     border-radius: var(--radius-sm);
     
     .req-label {
-      font-weight: 500;
+      font-weight: var(--font-weight-medium, 500);
       color: var(--text-secondary);
     }
     
     .req-value {
       font-family: 'Courier New', monospace;
       color: var(--text-primary);
-      font-weight: 600;
+      font-weight: var(--font-weight-semibold, 600);
     }
   }
 }
@@ -45,7 +45,7 @@
 }
 
 .org-name {
-  font-weight: 600;
+  font-weight: var(--font-weight-semibold, 600);
   color: var(--text-primary);
   margin-bottom: 0.75rem;
 }
@@ -73,7 +73,7 @@
 
     strong {
       color: var(--text-primary);
-      font-weight: 600;
+      font-weight: var(--font-weight-semibold, 600);
     }
 
     span {