feat: add a cli product for the gt documentation

gt, the Gitea CLI, gets its own product next to the runner: the CLI entry
in the header, its own sidebars, search scope, crawler start url and
redirects, and `make cut-version PRODUCT=cli`. Until a release series is
listed, the develop docs are served at /cli/ without the unreleased banner.

A directory with an index page and no _category_.json now takes its
sidebar label and position from that page, which leads the group, so the
generated reference can be grouped by command.

Signed-off-by: bircni <[email protected]>

cloudflare/docsearch-crawler.json

@@ -7,6 +7,7 @@
     "https://docs.gitea.com/zh-cn/",
     "https://docs.gitea.com/zh-tw/",
     "https://docs.gitea.com/runner/",
+    "https://docs.gitea.com/cli/",
     "https://docs.gitea.com/api/",
     "https://docs.gitea.com/enterprise/"
   ],
@@ -15,7 +16,8 @@
     "https://docs.gitea.com/1.2*/**",
     "https://docs.gitea.com/*/1.2*/**",
     "https://docs.gitea.com/api/1.2*/**",
-    "https://docs.gitea.com/runner/[0-9]/**"
+    "https://docs.gitea.com/runner/[0-9]/**",
+    "https://docs.gitea.com/cli/[0-9]*/**"
   ],
   "selectors": {
     "lvl0": { "selector": "//nav[contains(@aria-labelledby,'starlight__sidebar')]//a[@aria-current='page']/ancestor::details//summary//span", "type": "xpath", "global": true, "default_value": "Documentation" },