refactor(web/css): replace hardcoded colors with CSS custom properties

Adds new badge, gradient, and surface variables to css-variables.css,
then uses them across resolver-main.css and resolver-shell.css to
centralize theme values and simplify future color adjustments.

web/css/resolver-shell.css

@@ -23,7 +23,7 @@
     visibility: hidden;
     opacity: 0;
     color: var(--mr-text, #f3f3f3);
-    background: linear-gradient(180deg, rgba(38, 77, 50, 0.82), rgba(18, 35, 24, 0.88));
+    background: var(--mr-gradient-dock-preview);
     border: 2px solid rgba(114, 211, 138, 0.72);
     border-radius: var(--mr-radius-xl);
     box-shadow: inset 0 0 0 1px rgba(255, 255, 255, 0.04);
@@ -622,7 +622,7 @@
     max-width: 92px;
     padding: var(--mr-spacing-2) var(--mr-spacing-6);
     overflow: hidden;
-    color: #c9f5d2;
+    color: var(--mr-type-lora-text);
     font-size: var(--mr-font-xs);
     font-weight: 800;
     line-height: 1.2;