fix: use proxy.ts instead of middleware.ts for Next.js 16

* fix(edit_diagram): implement cascade delete for children and edges

- Add automatic cascade deletion when deleting a cell
- Recursively delete all child cells (parent attribute references)
- Delete all edges referencing deleted cells (source/target)
- Skip silently if cell already deleted (handles AI redundant ops)
- Update prompts to inform AI about cascade behavior

Fixes #450

* fix: add root cell protection and sync MCP server cascade delete

- Add protection for root cells '0' and '1' to prevent full diagram wipe
- Sync MCP server with main app's cascade delete logic
- Both lib/utils.ts and packages/mcp-server now have identical delete behavior

* chore(mcp): bump version to 0.1.9

* fix(cascade-delete): recursively collect edge children (labels)

- Change from cellsToDelete.add(edgeId) to collectDescendants(edgeId)
- Fixes orphaned edge labels causing draw.io to crash/clear canvas
- Edge labels (parent=edgeId) are now deleted with their parent edge

proxy.ts

@@ -0,0 +1,63 @@
+import { match as matchLocale } from "@formatjs/intl-localematcher"
+import Negotiator from "negotiator"
+import type { NextRequest } from "next/server"
+import { NextResponse } from "next/server"
+import { i18n } from "./lib/i18n/config"
+
+function getLocale(request: NextRequest): string | undefined {
+    // Negotiator expects plain object so we need to transform headers
+    const negotiatorHeaders: Record<string, string> = {}
+    request.headers.forEach((value, key) => {
+        negotiatorHeaders[key] = value
+    })
+
+    // @ts-expect-error locales are readonly
+    const locales: string[] = i18n.locales
+
+    // Use negotiator and intl-localematcher to get best locale
+    const languages = new Negotiator({ headers: negotiatorHeaders }).languages(
+        locales,
+    )
+
+    const locale = matchLocale(languages, locales, i18n.defaultLocale)
+
+    return locale
+}
+
+export function proxy(request: NextRequest) {
+    const pathname = request.nextUrl.pathname
+
+    // Skip API routes, static files, and Next.js internals
+    if (
+        pathname.startsWith("/api/") ||
+        pathname.startsWith("/_next/") ||
+        pathname.includes("/favicon") ||
+        /\.(.*)$/.test(pathname)
+    ) {
+        return
+    }
+
+    // Check if there is any supported locale in the pathname
+    const pathnameIsMissingLocale = i18n.locales.every(
+        (locale) =>
+            !pathname.startsWith(`/${locale}/`) && pathname !== `/${locale}`,
+    )
+
+    // Redirect if there is no locale
+    if (pathnameIsMissingLocale) {
+        const locale = getLocale(request)
+
+        // Redirect to localized path
+        return NextResponse.redirect(
+            new URL(
+                `/${locale}${pathname.startsWith("/") ? "" : "/"}${pathname}`,
+                request.url,
+            ),
+        )
+    }
+}
+
+export const config = {
+    // Matcher ignoring `/_next/` and `/api/`
+    matcher: ["/((?!api|_next/static|_next/image|favicon.ico).*)"],
+}