Redesign webapp with minimal style and full backend integration

- New monochrome design system in globals.css (no shadows, tight spacing, system-font)
- Root layout stripped to html/body; home page owns its Header/Footer
- Dashboard fully wired to FastAPI backend: upload, branch, submission, publish, download
- CVTree rebuilt as compact file-tree component driven by real version data
- DiffViewer rebuilt as minimal git-diff display using real patch data
- API client (libs/api.ts) extended with all CRUD operations
- Header redesigned to match minimal style
- Backend: added GET /documents/{id}/versions/{id}/download endpoint for DOCX export

https://claude.ai/code/session_01Xmxm2QLgFBgRJyYD6VukR6

apps/webapp/src/components/Header.tsx

@@ -1,53 +1,21 @@
 import Link from "next/link";
 
 export default function Header() {
-  return (
-    <header className="bg-white border-b border-gray-200 sticky top-0 z-40">
-      <div className="max-w-7xl mx-auto px-6 py-4">
-        <div className="flex items-center justify-between">
-          <div className="flex items-center">
-            <Link href="/" className="text-xl font-bold text-gray-900 hover:text-blue-600 transition-colors">
-              Resume Branches
+    return (
+        <header style={{ borderBottom: "1px solid var(--border)", padding: "0 24px", height: 52, display: "flex", alignItems: "center", justifyContent: "space-between", background: "#fff", position: "sticky", top: 0, zIndex: 40 }}>
+            <Link href="/" style={{ fontSize: 14, fontWeight: 600, color: "var(--text)", textDecoration: "none" }}>
+                Resume Branches
             </Link>
-          </div>
-          
-          <nav className="hidden md:flex items-center space-x-8">
-            <Link 
-              href="/" 
-              className="text-gray-600 hover:text-gray-900 font-medium transition-colors"
-            >
-              Home
-            </Link>
-            <Link 
-              href="/dashboard" 
-              className="text-gray-600 hover:text-gray-900 font-medium transition-colors"
-            >
-              Dashboard
-            </Link>
-            <Link 
-              href="/docs" 
-              className="text-gray-600 hover:text-gray-900 font-medium transition-colors"
-            >
-              Docs
-            </Link>
-          </nav>
-          
-          <div className="flex items-center gap-3">
-            <Link 
-              href="/login" 
-              className="text-gray-600 hover:text-gray-900 font-medium transition-colors"
-            >
-              Sign In
-            </Link>
-            <Link 
-              href="/dashboard" 
-              className="btn-primary"
-            >
-              Get Started
-            </Link>
-          </div>
-        </div>
-      </div>
-    </header>
-  );
+            <nav style={{ display: "flex", alignItems: "center", gap: 24 }}>
+                {[["Dashboard", "/dashboard"], ["Docs", "/docs"]].map(([label, href]) => (
+                    <Link key={href} href={href} style={{ fontSize: 13, color: "var(--text-muted)", textDecoration: "none" }}>
+                        {label}
+                    </Link>
+                ))}
+                <Link href="/dashboard" className="btn btn-primary" style={{ padding: "5px 14px", fontSize: 13 }}>
+                    Open app
+                </Link>
+            </nav>
+        </header>
+    );
 }