docs: restructure nav — drop FAQ/Changelog tabs, add API Reference tab

Remove the standalone FAQ and Changelog top-level tabs. FAQ and
Community pages move into the Overview tab as their own groups
(still fully reachable, just relocated). Changelog was only an
external link to GitHub releases and had no pages of its own.

Split the API reference pages (reference/*) out of the Modules tab
into a new, dedicated API Reference tab, so Modules now holds only
the conceptual guides and API Reference holds every module's class
and function documentation.

docs/docs.json

@@ -121,6 +121,23 @@
             "pages": [
               "vector_stores/pgvector"
             ]
+          },
+          {
+            "group": "FAQ",
+            "pages": [
+              "faq"
+            ]
+          },
+          {
+            "group": "Community",
+            "pages": [
+              "community",
+              "community-projects",
+              "contributing-guide",
+              "governance",
+              "citation",
+              "project-license"
+            ]
           }
         ]
       },
@@ -167,7 +184,17 @@
               "guides/policy-engine",
               "guides/visualization",
               "guides/distance-intelligence",
-              "guides/graph-analytics",
+              "guides/graph-analytics"
+            ]
+          }
+        ]
+      },
+      {
+        "tab": "API Reference",
+        "groups": [
+          {
+            "group": "Context & Intelligence",
+            "pages": [
               "reference/context",
               "reference/kg",
               "reference/temporal",
@@ -236,32 +263,6 @@
             ]
           }
         ]
-      },
-      {
-        "tab": "FAQ",
-        "groups": [
-          {
-            "group": "FAQ",
-            "pages": [
-              "faq"
-            ]
-          },
-          {
-            "group": "Community",
-            "pages": [
-              "community",
-              "community-projects",
-              "contributing-guide",
-              "governance",
-              "citation",
-              "project-license"
-            ]
-          }
-        ]
-      },
-      {
-        "tab": "Changelog",
-        "href": "https://github.com/semantica-agi/semantica/releases"
       }
     ]
   },