feat: dark-tech UI redesign + markdown patch cards

Redesign the frontend with a dark-tech theme: add Tailwind + PostCSS,
design tokens, and shadcn-style primitives (Button/Card/Input/Dialog/
DropdownMenu/Tabs/ScrollArea/etc.); restyle the app shell, navigation,
sidebar tree, content view, markdown rendering, editors, modals and
settings panels. Behavior/props unchanged; Font Awesome replaced with
lucide-react.

Add the patch cards feature UI: patch-queries hooks and a PatchCards
component rendered below the markdown body, with an Add Patch button
and create/edit dialog.

Fix tree expandability: folders with an index page now expand on name
click (and navigate), and the chevron+folder icon is one larger toggle.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/components/ui/scroll-area.js

@@ -0,0 +1,25 @@
+import React from "react";
+import * as ScrollAreaPrimitive from "@radix-ui/react-scroll-area";
+import { cn } from "../../lib/utils";
+
+const ScrollArea = React.forwardRef(({ className, children, ...props }, ref) => (
+    <ScrollAreaPrimitive.Root
+        ref={ref}
+        className={cn("relative overflow-hidden", className)}
+        {...props}
+    >
+        <ScrollAreaPrimitive.Viewport className="h-full w-full rounded-[inherit]">
+            {children}
+        </ScrollAreaPrimitive.Viewport>
+        <ScrollAreaPrimitive.Scrollbar
+            orientation="vertical"
+            className="flex w-2 touch-none select-none p-0.5 transition-colors"
+        >
+            <ScrollAreaPrimitive.Thumb className="relative flex-1 rounded-full bg-border" />
+        </ScrollAreaPrimitive.Scrollbar>
+        <ScrollAreaPrimitive.Corner />
+    </ScrollAreaPrimitive.Root>
+));
+ScrollArea.displayName = "ScrollArea";
+
+export { ScrollArea };