docs: fix broken links checker and add CI docs (#13041)

- Fix zh-CN/vps.md broken links (/railway  /install/railway)
- Add docs/ci.md explaining CI pipeline
- Add Experiments group to docs.json navigation

docs/docs.json

@@ -1232,6 +1232,16 @@
               {
                 "group": "Release notes",
                 "pages": ["reference/RELEASING", "reference/test"]
+              },
+              {
+                "group": "Experiments",
+                "pages": [
+                  "experiments/onboarding-config-protocol",
+                  "experiments/plans/cron-add-hardening",
+                  "experiments/plans/group-policy-hardening",
+                  "experiments/research/memory",
+                  "experiments/proposals/model-config"
+                ]
               }
             ]
           },
@@ -1751,6 +1761,16 @@
               {
                 "group": "发布说明",
                 "pages": ["zh-CN/reference/RELEASING", "zh-CN/reference/test"]
+              },
+              {
+                "group": "实验性功能",
+                "pages": [
+                  "zh-CN/experiments/onboarding-config-protocol",
+                  "zh-CN/experiments/plans/cron-add-hardening",
+                  "zh-CN/experiments/plans/group-policy-hardening",
+                  "zh-CN/experiments/research/memory",
+                  "zh-CN/experiments/proposals/model-config"
+                ]
               }
             ]
           },