style(ui): restore rounding for buttons, comments, and company/project icons

Per feedback on PAP-186: containers should have hard edges but buttons,
comment containers, project icons, and company icons should keep rounding.

- Restore --radius-sm (6px) and --radius-md (8px) for buttons/inputs
- Keep --radius-lg and --radius-xl at 0 for cards/containers/dialogs
- Add rounded-sm to comment container divs in CommentThread
- Replace rounded-xl with rounded-[14px] on company icons (CompanyRail,
  CompanySettings) since --radius-xl is 0
- Fix brand color dot in Sidebar (rounded → rounded-sm)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

ui/src/components/Sidebar.tsx

@@ -8,6 +8,7 @@ import {
   Search,
   SquarePen,
   Network,
+  Settings,
 } from "lucide-react";
 import { useQuery } from "@tanstack/react-query";
 import { SidebarSection } from "./SidebarSection";
@@ -46,6 +47,12 @@ export function Sidebar() {
     <aside className="w-60 h-full min-h-0 border-r border-border bg-background flex flex-col">
       {/* Top bar: Company name (bold) + Search — aligned with top sections (no visible border) */}
       <div className="flex items-center gap-1 px-3 h-12 shrink-0">
+        {selectedCompany?.brandColor && (
+          <div
+            className="w-4 h-4 rounded-sm shrink-0 ml-1"
+            style={{ backgroundColor: selectedCompany.brandColor }}
+          />
+        )}
         <span className="flex-1 text-sm font-bold text-foreground truncate pl-1">
           {selectedCompany?.name ?? "Select company"}
         </span>
@@ -94,6 +101,7 @@ export function Sidebar() {
             <SidebarNavItem to="/org" label="Org" icon={Network} />
             <SidebarNavItem to="/costs" label="Costs" icon={DollarSign} />
             <SidebarNavItem to="/activity" label="Activity" icon={History} />
+            <SidebarNavItem to="/company/settings" label="Settings" icon={Settings} />
           </SidebarSection>
         </nav>
       </ScrollArea>