refactor: rename loader/model packages to loaders/models

- Rename docforge.loader → docforge.loaders and docforge.model → docforge.models
- Update all imports, type stubs, CLI, tests, and documentation references
- Align MkDocs navigation and docforge.nav.yml with new package structure
- Adjust module docstrings and comments for consistency with pluralized naming

docforge/models/object.pyi

@@ -0,0 +1,27 @@
+from typing import Dict, Iterable, Optional
+
+
+class DocObject:
+    """Represents a documented Python object."""
+
+    name: str
+    kind: str
+    path: str
+    signature: Optional[str]
+    docstring: Optional[str]
+    members: Dict[str, "DocObject"]
+
+    def __init__(
+        self,
+        name: str,
+        kind: str,
+        path: str,
+        signature: Optional[str] = ...,
+        docstring: Optional[str] = ...,
+    ) -> None: ...
+
+    def add_member(self, obj: "DocObject") -> None: ...
+
+    def get_member(self, name: str) -> "DocObject": ...
+
+    def get_all_members(self) -> Iterable["DocObject"]: ...