docs: add wiki, complete lib nav, and rebuild mcp artifacts

- Add hand-written wiki (index, overview, how-to, extending, dev) with
  MkDocs config following the platform anatomy
- Complete the library nav by registering the csv and xlsx groups in
  docforge.nav.yml and docs/mkdocs.lib.yml
- Regenerate lib/MCP outputs with the rebuilt nav

docs/mcp/modules/omniread.core.content.json

@@ -4,39 +4,11 @@
     "path": "omniread.core.content",
     "docstring": "# Summary\n\nCanonical content models for OmniRead.\n\nThis module defines the **format-agnostic content representation** used across\nall parsers and scrapers in OmniRead.\n\nThe models defined here represent *what* was extracted, not *how* it was\nretrieved or parsed. Format-specific behavior and metadata must not alter\nthe semantic meaning of these models.",
     "objects": {
-      "Mapping": {
-        "name": "Mapping",
-        "kind": "alias",
-        "path": "omniread.core.content.Mapping",
-        "signature": "<bound method Alias.signature of Alias('Mapping', 'collections.abc.Mapping')>",
-        "docstring": null
-      },
-      "dataclass": {
-        "name": "dataclass",
-        "kind": "alias",
-        "path": "omniread.core.content.dataclass",
-        "signature": "<bound method Alias.signature of Alias('dataclass', 'dataclasses.dataclass')>",
-        "docstring": null
-      },
-      "Enum": {
-        "name": "Enum",
-        "kind": "alias",
-        "path": "omniread.core.content.Enum",
-        "signature": "<bound method Alias.signature of Alias('Enum', 'enum.Enum')>",
-        "docstring": null
-      },
-      "Any": {
-        "name": "Any",
-        "kind": "alias",
-        "path": "omniread.core.content.Any",
-        "signature": "<bound method Alias.signature of Alias('Any', 'typing.Any')>",
-        "docstring": null
-      },
       "ContentType": {
         "name": "ContentType",
         "kind": "class",
         "path": "omniread.core.content.ContentType",
-        "signature": "<bound method Class.signature of Class('ContentType', 20, 49)>",
+        "signature": null,
         "docstring": "Supported MIME types for extracted content.\n\nNotes:\n    **Guarantees:**\n\n        - This enum represents the declared or inferred media type of the\n          content source.\n        - It is primarily used for routing content to the appropriate\n          parser or downstream consumer.",
         "members": {
           "HTML": {
@@ -87,7 +59,7 @@
         "name": "Content",
         "kind": "class",
         "path": "omniread.core.content.Content",
-        "signature": "<bound method Class.signature of Class('Content', 52, 84)>",
+        "signature": "Content(raw: bytes, source: str, content_type: ContentType | None = ..., metadata: Mapping[str, Any] | None = ...)",
         "docstring": "Normalized representation of extracted content.\n\nNotes:\n    **Responsibilities:**\n\n        - A `Content` instance represents a raw content payload along with\n          minimal contextual metadata describing its origin and type.\n        - This class is the primary exchange format between scrapers,\n          parsers, and downstream consumers.",
         "members": {
           "raw": {