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/loaders/__init__.py

@@ -0,0 +1,22 @@
+"""
+# Loader Layer
+
+The `docforge.loaders` package is responsible for discovering Python source files
+and extracting their documentation using static analysis.
+
+## Core Features
+
+- **Discovery**: Automatically find all modules and packages in a project
+  directory.
+- **Introspection**: Uses `griffe` to parse docstrings, signatures, and
+  hierarchical relationships without executing the code.
+- **Filtering**: Automatically excludes private members (prefixed with `_`) to
+  ensure clean public documentation.
+"""
+
+from .griffe_loader import GriffeLoader, discover_module_paths
+
+__all__ = [
+    "GriffeLoader",
+    "discover_module_paths",
+]