fix: make MkDocs generation filesystem-complete and package-aware

- Add filesystem-based module discovery via `discover_module_paths`
- Decouple documentation coverage from Python import behavior
- Ensure GriffeLoader receives a full module list instead of a single root
- Make MkDocs renderer level-agnostic using global package detection
- Emit `index.md` only for true packages, suppress `<package>.md`
- Mirror full dotted module hierarchy into nested docs directories
- Update CLI, exports, and type stubs to expose discovery helper
- Align tests with filesystem-driven module coverage

This fixes missing docs for submodules and removes invalid package `.md` files.

docforge/loader/griffe_loader.py

@@ -1,6 +1,7 @@
 from __future__ import annotations
 
 import logging
+from pathlib import Path
 from typing import List, Optional
 
 from griffe import (
@@ -16,6 +17,41 @@ from docforge.model import Module, Project, DocObject
 logger = logging.getLogger(__name__)
 
 
+def discover_module_paths(
+    module_name: str,
+    project_root: Path | None = None,
+) -> List[str]:
+    """
+    Discover all Python modules under a package via filesystem traversal.
+
+    Rules:
+    - Directory with __init__.py => package
+    - .py file => module
+    - Paths converted to dotted module paths
+    """
+
+    if project_root is None:
+        project_root = Path.cwd()
+
+    pkg_dir = project_root / module_name
+    if not pkg_dir.exists():
+        raise FileNotFoundError(f"Package not found: {pkg_dir}")
+
+    module_paths: List[str] = []
+
+    for path in pkg_dir.rglob("*.py"):
+        if path.name == "__init__.py":
+            module_path = path.parent
+        else:
+            module_path = path
+
+        rel = module_path.relative_to(project_root)
+        dotted = ".".join(rel.with_suffix("").parts)
+        module_paths.append(dotted)
+
+    return sorted(set(module_paths))
+
+
 class GriffeLoader:
     """Loads Python modules using Griffe introspection."""