docs(develop): add single-page AI assistant context for developers (zh/en/ja)

docs.json

@@ -411,6 +411,7 @@
               {
                 "group": "Core Development",
                 "pages": [
+                  "en/develop/agent-context",
                   "en/develop/dev-config",
                   "en/develop/plugin-runtime",
                   "en/develop/comp-arch",
@@ -634,6 +635,7 @@
               {
                 "group": "核心开发",
                 "pages": [
+                  "zh/develop/agent-context",
                   "zh/develop/dev-config",
                   "zh/develop/plugin-runtime",
                   "zh/develop/comp-arch",
@@ -852,6 +854,7 @@
               {
                 "group": "コア開発",
                 "pages": [
+                  "ja/develop/agent-context",
                   "ja/develop/dev-config",
                   "ja/develop/plugin-runtime",
                   "ja/develop/comp-arch",