Add GEDCOM Import/Export UI (defaults to importing into a new tree)

An Import/Export page (sidebar) that defaults to importing into a NEW tree to avoid duplicating existing people, with an explicit 'append to this tree' option (warned), a mapping-report display (counts + skipped tags), and a one-click .ged export download.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Signed-off-by: Justin Paul <justin@jpaul.me>

frontend/components/app-sidebar.tsx

@@ -1,6 +1,14 @@
 "use client";
 
-import { Archive, BookText, FolderTree, Image as ImageIcon, LogOut, Users } from "lucide-react";
+import {
+  Archive,
+  ArrowDownUp,
+  BookText,
+  FolderTree,
+  Image as ImageIcon,
+  LogOut,
+  Users,
+} from "lucide-react";
 import Link from "next/link";
 import { usePathname, useRouter } from "next/navigation";
 import { useEffect, useState } from "react";
@@ -87,6 +95,12 @@ export function AppSidebar() {
             icon={ImageIcon}
             active={pathname.startsWith(`/trees/${treeId}/media`)}
           />
+          <Item
+            href={`/trees/${treeId}/gedcom`}
+            label="Import / Export"
+            icon={ArrowDownUp}
+            active={pathname.startsWith(`/trees/${treeId}/gedcom`)}
+          />
           <Item
             href={`/trees/${treeId}/recovery`}
             label="Recovery"