feat: upgrade team admin with click-to-edit, Instagram validation, date picker, city autocomplete

- Team list: click card to open editor (remove pencil button), keep drag-to-reorder
- Instagram field: username-only input with @ prefix, async account validation via HEAD request
- Victory dates: date range picker replacing text input, auto-formats to DD.MM.YYYY / DD-DD.MM.YYYY
- Victory location: city autocomplete via Nominatim API with suggestions dropdown
- Links: real-time URL validation with error indicators on all link fields
- Save button blocked when any validation errors exist

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/app/api/admin/validate-instagram/route.ts

@@ -0,0 +1,27 @@
+import { NextRequest, NextResponse } from "next/server";
+
+export async function GET(request: NextRequest) {
+  const username = request.nextUrl.searchParams.get("username")?.trim();
+  if (!username) {
+    return NextResponse.json({ valid: false, error: "No username" });
+  }
+
+  try {
+    const res = await fetch(`https://www.instagram.com/${username}/`, {
+      method: "HEAD",
+      redirect: "follow",
+      headers: {
+        "User-Agent":
+          "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/120.0.0.0 Safari/537.36",
+      },
+      signal: AbortSignal.timeout(5000),
+    });
+
+    // Instagram returns 200 for existing profiles, 404 for non-existing
+    const valid = res.ok;
+    return NextResponse.json({ valid });
+  } catch {
+    // Network error or timeout — don't block the user
+    return NextResponse.json({ valid: true, uncertain: true });
+  }
+}