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/collapsible.tsx

@@ -0,0 +1,21 @@
+"use client"
+
+import { Collapsible as CollapsiblePrimitive } from "@base-ui/react/collapsible"
+
+function Collapsible({ ...props }: CollapsiblePrimitive.Root.Props) {
+  return <CollapsiblePrimitive.Root data-slot="collapsible" {...props} />
+}
+
+function CollapsibleTrigger({ ...props }: CollapsiblePrimitive.Trigger.Props) {
+  return (
+    <CollapsiblePrimitive.Trigger data-slot="collapsible-trigger" {...props} />
+  )
+}
+
+function CollapsibleContent({ ...props }: CollapsiblePrimitive.Panel.Props) {
+  return (
+    <CollapsiblePrimitive.Panel data-slot="collapsible-content" {...props} />
+  )
+}
+
+export { Collapsible, CollapsibleTrigger, CollapsibleContent }