📩 fix: Restore Primary Action Button Visibility in Light Mode (#12591)

The default <Button> variant (bg-primary / text-primary-foreground)
renders invisible in light mode on the Agent Marketplace 'Start Chat'
button and the Grant Access dialog 'Save Changes' button, making these
primary actions undiscoverable without hovering.

Switch these three affirmative-action buttons to variant='submit',
which uses the hardcoded 'bg-surface-submit text-white' combination
already defined in the Button component specifically to avoid the
contrast issues of the default variant (see the comment above the
'submit' variant in packages/client/src/components/Button.tsx).

No visual change in dark mode; in light mode the buttons now render
as the green submit color with white text, matching the semantic
intent of the action.

Co-authored-by: Timothy Look <timothy.look@pmv.eu>

client/src/components/Agents/AgentDetail.tsx

@@ -183,7 +183,12 @@ const AgentDetail: React.FC<AgentDetailProps> = ({ agent, isOpen, onClose }) =>
           >
             <Link className="h-4 w-4" aria-hidden="true" />
           </Button>
-          <Button className="w-full max-w-xs" onClick={handleStartChat} disabled={!agent}>
+          <Button
+            variant="submit"
+            className="w-full max-w-xs"
+            onClick={handleStartChat}
+            disabled={!agent}
+          >
             {localize('com_agents_start_chat')}
           </Button>
         </div>

client/src/components/Agents/AgentDetailContent.tsx

@@ -181,7 +181,12 @@ const AgentDetailContent: React.FC<AgentDetailContentProps> = ({ agent }) => {
         >
           <Link className="h-4 w-4" aria-hidden="true" />
         </Button>
-        <Button className="w-full max-w-xs" onClick={handleStartChat} disabled={!agent}>
+        <Button
+          variant="submit"
+          className="w-full max-w-xs"
+          onClick={handleStartChat}
+          disabled={!agent}
+        >
           {localize('com_agents_start_chat')}
         </Button>
       </div>

client/src/components/Sharing/GenericGrantAccessDialog.tsx

@@ -401,6 +401,7 @@ export default function GenericGrantAccessDialog({
                 </Button>
               </OGDialogClose>
               <Button
+                variant="submit"
                 onClick={handleSave}
                 disabled={
                   updatePermissionsMutation.isLoading ||