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/components/search-dialog.tsx

@@ -0,0 +1,56 @@
+'use client';
+
+import { create } from '@orama/orama';
+import { useDocsSearch } from 'fumadocs-core/search/client';
+import { oramaStaticClient } from 'fumadocs-core/search/client/orama-static';
+import {
+  SearchDialog,
+  SearchDialogClose,
+  SearchDialogContent,
+  SearchDialogHeader,
+  SearchDialogIcon,
+  SearchDialogInput,
+  SearchDialogList,
+  SearchDialogOverlay,
+} from 'fumadocs-ui/components/dialog/search';
+import { useI18n } from 'fumadocs-ui/contexts/i18n';
+import { useMemo } from 'react';
+
+interface SharedProps {
+  open: boolean;
+  onOpenChange: (open: boolean) => void;
+}
+
+// The static search index is keyed by locale code (en/fa/ru/zh). Fumadocs'
+// default static dialog feeds those codes to Orama as a tokenizer language, but
+// Orama only accepts full names ("english") and throws on "en" — which silently
+// breaks search entirely. All docs content is English (other locales fall back
+// to it), so re-create the dialog — the documented escape hatch for custom Orama
+// setups — with an initOrama that always builds an English index.
+export default function SearchDialogClient(props: SharedProps) {
+  const { locale } = useI18n();
+  const client = useMemo(
+    () =>
+      oramaStaticClient({
+        from: '/api/search',
+        locale,
+        initOrama: () => create({ schema: { _: 'string' }, language: 'english' }),
+      }),
+    [locale],
+  );
+  const { search, setSearch, query } = useDocsSearch({ client });
+
+  return (
+    <SearchDialog search={search} onSearchChange={setSearch} isLoading={query.isLoading} {...props}>
+      <SearchDialogOverlay />
+      <SearchDialogContent>
+        <SearchDialogHeader>
+          <SearchDialogIcon />
+          <SearchDialogInput />
+          <SearchDialogClose />
+        </SearchDialogHeader>
+        <SearchDialogList items={query.data !== 'empty' ? query.data : null} />
+      </SearchDialogContent>
+    </SearchDialog>
+  );
+}