feat: list each declared doc kind as its own homepage card

- compute per-kind home URLs (lib/, api/, wiki/) via _find_home_for_kind
- emit one card per declared kind so multi-kind repos (e.g. doc-forge
  with lib + wiki) appear in each matching homepage section
- declare the doc-forge wiki kind and refresh its vendored site with the
  combined lib + wiki build

doc-forge/mcp/nav.json

@@ -7,6 +7,10 @@
     "module": "docforge.cli",
     "resource": "doc://modules/docforge.cli"
   },
+  {
+    "module": "docforge.cli.api_utils",
+    "resource": "doc://modules/docforge.cli.api_utils"
+  },
   {
     "module": "docforge.cli.commands",
     "resource": "doc://modules/docforge.cli.commands"