feat(ui): Discord-style roles/channel perms + IDE themes

Split-pane role editor with tri-state channel overrides (roles/members).
CSS-var themes (Gruvbox default + 9 IDE palettes) in top bar and settings.

web/src/components/ServerSettingsModal.tsx

@@ -210,7 +210,7 @@ export function ServerSettingsModal({ serverId, onClose }: ServerSettingsModalPr
       onClick={handleClose}
     >
       <div
-        className="bg-gb-bg border border-gb-bg-t w-[750px] max-h-[85vh] flex flex-col font-mono"
+        className="bg-gb-bg border border-gb-bg-t w-[min(920px,95vw)] max-h-[85vh] flex flex-col font-mono"
         onClick={(e) => e.stopPropagation()}
       >
         <div className="flex items-center justify-between px-4 py-3 border-b border-gb-bg-t">
@@ -342,7 +342,7 @@ export function ServerSettingsModal({ serverId, onClose }: ServerSettingsModalPr
           )}
 
           {tab === 'roles' && (
-            <div className="h-[60vh] overflow-y-auto">
+            <div className="h-[60vh] -m-4">
               <RoleManager serverId={serverId} />
             </div>
           )}