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/Markdowns/MarkdownContent.css

@@ -1,42 +1 @@
-.markdown-content-container {
-    margin: 20px;
-    padding: 20px;
-    background: #fff;
-    border-radius: 8px;
-    box-shadow: 0 2px 5px rgba(0, 0, 0, 0.1);
-}
-
-.markdown-content {
-    font-family: "Arial", sans-serif;
-    line-height: 1.6;
-}
-
-.markdown-content pre {
-    background: #f5f5f5;
-    padding: 10px;
-    border-radius: 4px;
-    overflow-x: auto;
-}
-
-.markdown-content code {
-    background: #f9f9f9;
-    padding: 2px 4px;
-    border-radius: 4px;
-    font-size: 0.95em;
-}
-.markdown-content-container-header {
-    align-items: center;
-    display: flex;
-    justify-content: space-between;
-}
-.markdown-content-container-header h1 {
-    margin: 0;
-    font-size: 1.5rem;
-    line-height: 1.5;
-}
-.markdown-content-container-header .button {
-    margin-left: auto;
-    height: auto;
-    display: inline-flex;
-    align-items: center;
-}
+/* Styling now lives in the components via Tailwind + MarkdownView.css. */