docs: modernize gateway configuration page (Phase 1) (#14111)

* docs(configuration): split into overview + full reference with Mintlify components

* docs(configuration): use tooltip for JSON5 format note

* docs(configuration): fix Accordion closing tags inside list contexts

* docs(configuration): expand intro to reflect full config surface

* docs(configuration): trim intro to three concise bullets

* docs(configuration-examples): revert all branch changes

* docs(configuration): improve hot-reload section with tabs and accordion

* docs(configuration): uncramp hot-reload — subheadings, bullet list, warning

* docs(configuration): restore hot-apply vs restart table

* docs(configuration): fix hot-reload table against codebase

* docs: add configuration-reference.md — full field-by-field reference

* docs(gateway): refresh runbook and align config reference

* docs: include pending docs updates and install graphic

docs/docs.json

@@ -24,6 +24,14 @@
     "dark": "#FF5A36",
     "light": "#FF8A6B"
   },
+  "styling": {
+    "codeblocks": {
+      "theme": {
+        "dark": "min-dark",
+        "light": "min-light"
+      }
+    }
+  },
   "navbar": {
     "links": [
       {
@@ -1100,6 +1108,7 @@
                     "group": "Configuration and operations",
                     "pages": [
                       "gateway/configuration",
+                      "gateway/configuration-reference",
                       "gateway/configuration-examples",
                       "gateway/authentication",
                       "gateway/health",