fix(ui): declare Material system tokens and migrate dead --mdc overrides (#1775)

.github/workflows/ci.yml

@@ -375,6 +375,9 @@ jobs:
             - name: Validate stylesheet Nx inputs
               run: pnpm run styles:inputs:validate
 
+            - name: Validate Angular Material token overrides
+              run: pnpm run styles:material-tokens:validate
+
             # Nx rejects a non-parallel task with continuous dependencies, and
             # the Playwright plugin infers serve dependencies only when CI is
             # unset, so this checks both the local and the CI inference.