docs(types): document the fixeds and ptrs typed buffers

The type table lists fixeds (buffer of fixed values) and ptrs (buffer of
pointers) alongside words, but they had no reference pages. Add both, with
compilable examples; coverage inventory updated (types: 10 -> 12).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

tools/docgen/inventory.json

@@ -173,15 +173,17 @@
     "kw-enum"
   ],
   "types": [
-    "type-int",
-    "type-fixed",
     "type-bool",
-    "type-str",
-    "type-entity",
-    "type-ptr",
-    "type-words",
     "type-byte",
+    "type-entity",
+    "type-fixed",
+    "type-fixeds",
+    "type-int",
+    "type-ptr",
+    "type-ptrs",
+    "type-slices",
+    "type-str",
     "type-void",
-    "type-slices"
+    "type-words"
   ]
 }