Build temetro app: dark theme, clinical sidebar, AI chat, settings page

- Linear-inspired dark theme (app/globals.css), forced dark in layout
- Clinical sidebar (components/sidebar-02) with temetro brand
- AI chat UI (components/chat): Cursor-style input, UI-only mock replies
- Settings page (components/settings): Polar-style tabs/sections, UI only
- Route-group app shell: app/(app)/{layout,page,settings}
- shadcn (Base UI) + ai-elements component libraries
- CLAUDE.md: architecture notes + per-folder commit policy

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

frontend/components/ui/button-group.tsx

@@ -0,0 +1,87 @@
+import { mergeProps } from "@base-ui/react/merge-props"
+import { useRender } from "@base-ui/react/use-render"
+import { cva, type VariantProps } from "class-variance-authority"
+
+import { cn } from "@/lib/utils"
+import { Separator } from "@/components/ui/separator"
+
+const buttonGroupVariants = cva(
+  "flex w-fit items-stretch *:focus-visible:relative *:focus-visible:z-10 has-[>[data-slot=button-group]]:gap-2 has-[>[data-variant=outline]]:*:data-[slot=input-group]:border-border has-[>[data-variant=outline]]:*:data-[slot=select-trigger]:border-border has-[>[data-variant=outline]]:[&>[data-slot=input-group]:has(:focus-visible)]:border-ring has-[>[data-variant=outline]]:[&>[data-slot=select-trigger]:focus-visible]:border-ring has-[select[aria-hidden=true]:last-child]:[&>[data-slot=select-trigger]:last-of-type]:rounded-r-4xl [&>[data-slot=select-trigger]:not([class*='w-'])]:w-fit [&>input]:flex-1 has-[>[data-variant=outline]]:[&>input]:border-border has-[>[data-variant=outline]]:[&>input:focus-visible]:border-ring",
+  {
+    variants: {
+      orientation: {
+        horizontal:
+          "*:data-slot:rounded-r-none [&>[data-slot]:not(:has(~[data-slot]))]:rounded-r-4xl! [&>[data-slot]~[data-slot]]:rounded-l-none [&>[data-slot]~[data-slot]]:border-l-0",
+        vertical:
+          "flex-col *:data-slot:rounded-b-none [&>[data-slot]:not(:has(~[data-slot]))]:rounded-b-4xl! [&>[data-slot]~[data-slot]]:rounded-t-none [&>[data-slot]~[data-slot]]:border-t-0",
+      },
+    },
+    defaultVariants: {
+      orientation: "horizontal",
+    },
+  }
+)
+
+function ButtonGroup({
+  className,
+  orientation,
+  ...props
+}: React.ComponentProps<"div"> & VariantProps<typeof buttonGroupVariants>) {
+  return (
+    <div
+      role="group"
+      data-slot="button-group"
+      data-orientation={orientation}
+      className={cn(buttonGroupVariants({ orientation }), className)}
+      {...props}
+    />
+  )
+}
+
+function ButtonGroupText({
+  className,
+  render,
+  ...props
+}: useRender.ComponentProps<"div">) {
+  return useRender({
+    defaultTagName: "div",
+    props: mergeProps<"div">(
+      {
+        className: cn(
+          "flex items-center gap-2 rounded-4xl border bg-muted px-2.5 text-sm font-medium [&_svg]:pointer-events-none [&_svg:not([class*='size-'])]:size-4",
+          className
+        ),
+      },
+      props
+    ),
+    render,
+    state: {
+      slot: "button-group-text",
+    },
+  })
+}
+
+function ButtonGroupSeparator({
+  className,
+  orientation = "vertical",
+  ...props
+}: React.ComponentProps<typeof Separator>) {
+  return (
+    <Separator
+      data-slot="button-group-separator"
+      orientation={orientation}
+      className={cn(
+        "relative self-stretch bg-input data-horizontal:mx-px data-horizontal:w-auto data-vertical:my-px data-vertical:h-auto",
+        className
+      )}
+      {...props}
+    />
+  )
+}
+
+export {
+  ButtonGroup,
+  ButtonGroupSeparator,
+  ButtonGroupText,
+  buttonGroupVariants,
+}