refactor(ui): drop redundant dark: colour overrides

The colour-token migration collapsed light/dark palette pairs (e.g.
text-red-600 dark:text-red-400) onto a single semantic token, leaving
no-op dark: duplicates (text-error dark:text-error). Semantic tokens are
already theme-aware, so the dark: variants are redundant. Also dropped the
dark:bg-background-*-subtle/NN opacity overrides — a raw-palette-era hack
(blue-950 was too saturated in dark); the dark-safe -subtle token is the
intended dark surface on its own. Kept genuinely-different variants.

Author: c-julin

frontend/src/components/ai-elements/message.tsx

@@ -106,7 +106,7 @@ export const MessageTimestamp = ({
       className={cn(
         "mt-2 text-xs",
         from === "user"
-          ? "text-informative dark:text-informative"
+          ? "text-informative"
           : "text-slate-500 dark:text-slate-400",
         className
       )}

frontend/src/components/pages/agents/details/ai-agent-card-tab.tsx

@@ -611,14 +611,12 @@ export const AIAgentCardTab = () => {
               )}
             </div>
 
-            <div className="rounded-md border border-outline-informative bg-background-informative-subtle p-3 dark:border-outline-informative dark:bg-background-informative-subtle/30">
+            <div className="rounded-md border border-outline-informative bg-background-informative-subtle p-3">
               <div className="flex gap-2">
-                <AlertCircle className="h-4 w-4 flex-shrink-0 text-informative dark:text-informative" />
+                <AlertCircle className="h-4 w-4 flex-shrink-0 text-informative" />
                 <div className="flex-1 space-y-1">
-                  <Text className="font-semibold text-informative text-sm dark:text-informative">
-                    Authentication Required
-                  </Text>
-                  <Text className="text-informative text-sm dark:text-informative">
+                  <Text className="font-semibold text-informative text-sm">Authentication Required</Text>
+                  <Text className="text-informative text-sm">
                     This agent requires a Redpanda Cloud M2M token for authentication.{' '}
                     <a className="underline" href="/organization-iam?tab=service-accounts">
                       Create an M2M token

frontend/src/components/pages/agents/details/ai-agent-inspector-tab.tsx

@@ -191,8 +191,8 @@ export const AIAgentInspectorTab = () => {
 
                 if (cardError) {
                   return (
-                    <div className="rounded-md border border-outline-error bg-background-error-subtle p-4 dark:border-outline-error dark:bg-background-error-subtle/30">
-                      <Text className="text-error dark:text-error">{cardError}</Text>
+                    <div className="rounded-md border border-outline-error bg-background-error-subtle p-4">
+                      <Text className="text-error">{cardError}</Text>
                     </div>
                   );
                 }

frontend/src/components/pages/mcp-servers/details/remote-mcp-connection-tab.tsx

@@ -94,14 +94,12 @@ export const RemoteMCPConnectionTab = () => {
                 <div className="w-full">
                   <DynamicCodeBlock code={mcpServerData?.mcpServer?.url || ''} lang="text" />
                 </div>
-                <div className="rounded-md border border-outline-informative bg-background-informative-subtle p-3 dark:border-outline-informative dark:bg-background-informative-subtle/30">
+                <div className="rounded-md border border-outline-informative bg-background-informative-subtle p-3">
                   <div className="flex items-start gap-2">
-                    <AlertCircle className="mt-0.5 h-4 w-4 flex-shrink-0 text-informative dark:text-informative" />
+                    <AlertCircle className="mt-0.5 h-4 w-4 flex-shrink-0 text-informative" />
                     <div className="space-y-2 text-sm">
-                      <Text className="font-medium text-informative dark:text-informative">
-                        Authentication Required
-                      </Text>
-                      <Text className="text-informative dark:text-informative">
+                      <Text className="font-medium text-informative">Authentication Required</Text>
+                      <Text className="text-informative">
                         This server requires a Redpanda Cloud M2M token for authentication.
                         <Link className="ml-1" href="/organization-iam?tab=service-accounts">
                           Create an M2M token here.

frontend/src/components/pages/mcp-servers/details/remote-mcp-inspector-tab.tsx

@@ -604,11 +604,11 @@ export const RemoteMCPInspectorTab = () => {
                         <div className="space-y-2">
                           {Object.entries(validationErrors).map(([field, error]) => (
                             <div
-                              className="rounded-md border border-outline-error bg-background-error-subtle p-3 dark:border-outline-error dark:bg-background-error-subtle/20"
+                              className="rounded-md border border-outline-error bg-background-error-subtle p-3"
                               key={field}
                             >
                               <div className="flex items-start">
-                                <Text className="text-error dark:text-error" variant="small">
+                                <Text className="text-error" variant="small">
                                   <Text as="span" className="font-medium">
                                     {field}:
                                   </Text>{' '}

frontend/src/components/pages/mcp-servers/details/remote-mcp-tool-button.tsx

@@ -40,10 +40,10 @@ export const RemoteMCPToolButton = ({
 }: RemoteMCPToolButtonProps) => {
   const getButtonClassName = () => {
     if (hasLintIssues) {
-      return 'border-outline-error bg-background-error-subtle dark:border-outline-error dark:bg-background-error-subtle/30';
+      return 'border-outline-error bg-background-error-subtle';
     }
     if (isSelected) {
-      return 'border-outline-informative bg-background-informative-subtle dark:border-outline-informative dark:bg-background-informative-subtle/30';
+      return 'border-outline-informative bg-background-informative-subtle';
     }
     return 'border-border bg-card hover:bg-gray-50 dark:hover:bg-secondary';
   };
@@ -71,7 +71,7 @@ export const RemoteMCPToolButton = ({
           </Text>
           {Boolean(hasLintIssues) && (
             <span title="Has linting issues">
-              <AlertCircle className="h-4 w-4 flex-shrink-0 text-error dark:text-error" />
+              <AlertCircle className="h-4 w-4 flex-shrink-0 text-error" />
             </span>
           )}
         </div>