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/utils/queries/patch-queries.js

@@ -0,0 +1,61 @@
+import { useQuery, useMutation, useQueryClient } from '@tanstack/react-query';
+import { fetch_ } from "../request-utils";
+import { useConfig } from "../../ConfigProvider";
+
+export const usePatches = (markdownId) => {
+    const config = useConfig();
+    return useQuery({
+        queryKey: ["patches", markdownId],
+        queryFn: () =>
+            fetch_(`${config.BACKEND_HOST}/api/patch/by_markdown/${markdownId}`),
+        enabled: !!markdownId,
+    });
+};
+
+export const useCreatePatch = () => {
+    const queryClient = useQueryClient();
+    const config = useConfig();
+    return useMutation({
+        mutationFn: (data) =>
+            fetch_(`${config.BACKEND_HOST}/api/patch/`, {
+                method: "POST",
+                body: JSON.stringify(data),
+            }),
+        onSuccess: (res) => {
+            queryClient.invalidateQueries({
+                queryKey: ["patches", res.markdown_id],
+            });
+        },
+    });
+};
+
+export const useUpdatePatch = () => {
+    const queryClient = useQueryClient();
+    const config = useConfig();
+    return useMutation({
+        mutationFn: ({ id, data }) =>
+            fetch_(`${config.BACKEND_HOST}/api/patch/${id}`, {
+                method: "PATCH",
+                body: JSON.stringify(data),
+            }),
+        onSuccess: (res) => {
+            queryClient.invalidateQueries({
+                queryKey: ["patches", res.markdown_id],
+            });
+        },
+    });
+};
+
+export const useDeletePatch = () => {
+    const queryClient = useQueryClient();
+    const config = useConfig();
+    return useMutation({
+        mutationFn: ({ id }) =>
+            fetch_(`${config.BACKEND_HOST}/api/patch/${id}`, {
+                method: "DELETE",
+            }),
+        onSuccess: (_res, { markdownId }) => {
+            queryClient.invalidateQueries({ queryKey: ["patches", markdownId] });
+        },
+    });
+};