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/dropdown-menu.js

@@ -0,0 +1,72 @@
+import React from "react";
+import * as DropdownMenuPrimitive from "@radix-ui/react-dropdown-menu";
+import { cn } from "../../lib/utils";
+
+const DropdownMenu = DropdownMenuPrimitive.Root;
+const DropdownMenuTrigger = DropdownMenuPrimitive.Trigger;
+const DropdownMenuGroup = DropdownMenuPrimitive.Group;
+
+const DropdownMenuContent = React.forwardRef(
+    ({ className, sideOffset = 6, ...props }, ref) => (
+        <DropdownMenuPrimitive.Portal>
+            <DropdownMenuPrimitive.Content
+                ref={ref}
+                sideOffset={sideOffset}
+                className={cn(
+                    "z-50 min-w-[12rem] overflow-hidden rounded-md border border-border bg-card p-1 text-card-foreground shadow-glow animate-fade-in",
+                    className
+                )}
+                {...props}
+            />
+        </DropdownMenuPrimitive.Portal>
+    )
+);
+DropdownMenuContent.displayName = "DropdownMenuContent";
+
+const DropdownMenuItem = React.forwardRef(
+    ({ className, inset, ...props }, ref) => (
+        <DropdownMenuPrimitive.Item
+            ref={ref}
+            className={cn(
+                "relative flex cursor-pointer select-none items-center gap-2 rounded-sm px-2 py-1.5 text-sm outline-none transition-colors",
+                "focus:bg-accent focus:text-foreground data-[disabled]:pointer-events-none data-[disabled]:opacity-50",
+                "[&_svg]:size-4 [&_svg]:text-muted-foreground focus:[&_svg]:text-primary",
+                inset && "pl-8",
+                className
+            )}
+            {...props}
+        />
+    )
+);
+DropdownMenuItem.displayName = "DropdownMenuItem";
+
+const DropdownMenuLabel = React.forwardRef(({ className, ...props }, ref) => (
+    <DropdownMenuPrimitive.Label
+        ref={ref}
+        className={cn(
+            "px-2 py-1.5 font-mono text-xs uppercase tracking-wide text-muted-foreground",
+            className
+        )}
+        {...props}
+    />
+));
+DropdownMenuLabel.displayName = "DropdownMenuLabel";
+
+const DropdownMenuSeparator = React.forwardRef(({ className, ...props }, ref) => (
+    <DropdownMenuPrimitive.Separator
+        ref={ref}
+        className={cn("-mx-1 my-1 h-px bg-border", className)}
+        {...props}
+    />
+));
+DropdownMenuSeparator.displayName = "DropdownMenuSeparator";
+
+export {
+    DropdownMenu,
+    DropdownMenuTrigger,
+    DropdownMenuContent,
+    DropdownMenuItem,
+    DropdownMenuLabel,
+    DropdownMenuSeparator,
+    DropdownMenuGroup,
+};