docs: vendor the documentation site into the monorepo

Fold the standalone 3x-ui-docs project (Next.js 16 + Fumadocs, deployed to
docs.sanaei.dev) into docs/ so the panel and its documentation share a single
source of truth, the way sing-box keeps its docs in-tree. The old repo becomes
redundant and can be retired.

- Import the full site under docs/ (app, components, content, lib, public,
  scripts, config). The self-contained pnpm project sits alongside the existing
  engineering notes with no filename collisions.
- Re-point "Edit on GitHub" links from MHSanaei/3x-ui-docs to this repo's
  docs/content/docs path (docs/lib/shared.ts, docs/app/.../page.tsx).
- Add docs-ci.yml and docs-deploy.yml under .github/workflows/, scoped to
  docs/** and run with working-directory: docs, since GitHub only runs
  workflows from the repo-root .github/. deploy-static.yml's GitHub Pages
  publish (CNAME docs.sanaei.dev) carries over unchanged.

Follow-up (outside this commit): attach the docs.sanaei.dev custom domain to
this repository's Pages (or set the Vercel project's root directory to docs),
confirm the site is live from the monorepo, then delete MHSanaei/3x-ui-docs.

docs/lib/xray/base64.ts

@@ -0,0 +1,42 @@
+// Browser- and Node-safe base64 / base64url helpers used by the in-browser
+// config tools. No Node `Buffer` so the same code runs in the browser and in
+// vitest (Node). `btoa`/`atob` and `TextEncoder`/`TextDecoder` are available in
+// both environments.
+
+export function bytesToBase64(bytes: Uint8Array): string {
+  let binary = '';
+  for (let i = 0; i < bytes.length; i++) binary += String.fromCharCode(bytes[i]);
+  return btoa(binary);
+}
+
+/** Decode standard or URL-safe base64, tolerating missing padding. */
+export function base64ToBytes(b64: string): Uint8Array {
+  const normalized = b64.replace(/-/g, '+').replace(/_/g, '/').replace(/\s/g, '');
+  const padded = normalized.padEnd(Math.ceil(normalized.length / 4) * 4, '=');
+  const binary = atob(padded);
+  const out = new Uint8Array(binary.length);
+  for (let i = 0; i < binary.length; i++) out[i] = binary.charCodeAt(i);
+  return out;
+}
+
+/** Encode bytes as URL-safe base64 with no padding (xray's key format). */
+export function bytesToBase64Url(bytes: Uint8Array): string {
+  return bytesToBase64(bytes).replace(/\+/g, '-').replace(/\//g, '_').replace(/=+$/, '');
+}
+
+export function base64UrlToBytes(s: string): Uint8Array {
+  return base64ToBytes(s);
+}
+
+const encoder = new TextEncoder();
+const decoder = new TextDecoder();
+
+/** UTF-8 text → standard base64 (used by vmess:// links). */
+export function textToBase64(text: string): string {
+  return bytesToBase64(encoder.encode(text));
+}
+
+/** standard/URL-safe base64 → UTF-8 text. */
+export function base64ToText(b64: string): string {
+  return decoder.decode(base64ToBytes(b64));
+}