fix(loaders): render clean signatures, drop unresolvable aliases from models

- Stringify Object.signature() instead of str()-ing the bound method,
  which produced "<bound method Class.signature of ...>" reprs
- Skip alias members that cannot resolve (stdlib/third-party imports)
  while preserving resolvable package re-exports; return None for empty
  signatures (classes without __init__ args)
- Add MCP renderer regression tests for signature cleanliness, alias
  filtering, and package re-export preservation

tests/renderers/mcp/test_mcp_signatures.py

@@ -0,0 +1,73 @@
+import json
+from pathlib import Path
+
+from docforge import MCPRenderer
+from docforge.loaders import GriffeLoader, discover_module_paths
+
+
+def _load_docforge_bundle(tmp_path: Path) -> Path:
+    project_root = Path(__file__).resolve().parents[3]
+    loader = GriffeLoader()
+    paths = discover_module_paths("docforge", project_root=project_root)
+    project = loader.load_project(paths)
+
+    out_dir = tmp_path / "mcp"
+    MCPRenderer().generate_sources(project, out_dir)
+    return out_dir
+
+
+def test_mcp_signatures_are_clean(tmp_path: Path) -> None:
+    out_dir = _load_docforge_bundle(tmp_path)
+
+    object_payload = json.loads(
+        (out_dir / "modules" / "docforge.models.object.json").read_text(
+            encoding="utf-8"
+        )
+    )
+
+    cls = object_payload["content"]["objects"]["DocObject"]
+    assert isinstance(cls["signature"], str)
+    assert "bound method" not in cls["signature"]
+    assert cls["signature"].startswith("DocObject(")
+
+    renderer_payload = json.loads(
+        (out_dir / "modules" / "docforge.renderers.mcp_renderer.json").read_text(
+            encoding="utf-8"
+        )
+    )
+
+    method = renderer_payload["content"]["objects"]["MCPRenderer"]["members"][
+        "generate_sources"
+    ]
+    assert isinstance(method["signature"], str)
+    assert "bound method" not in method["signature"]
+    assert method["signature"].startswith("generate_sources(")
+
+
+def test_mcp_skips_unresolvable_import_aliases(tmp_path: Path) -> None:
+    out_dir = _load_docforge_bundle(tmp_path)
+
+    renderer_payload = json.loads(
+        (out_dir / "modules" / "docforge.renderers.mcp_renderer.json").read_text(
+            encoding="utf-8"
+        )
+    )
+
+    object_names = set(renderer_payload["content"]["objects"])
+    assert "json" not in object_names
+    assert "Path" not in object_names
+
+
+def test_mcp_keeps_resolvable_package_reexports(tmp_path: Path) -> None:
+    out_dir = _load_docforge_bundle(tmp_path)
+
+    root_payload = json.loads(
+        (out_dir / "modules" / "docforge.json").read_text(encoding="utf-8")
+    )
+
+    discover = root_payload["content"]["objects"]["discover_module_paths"]
+    assert discover["name"] == "discover_module_paths"
+    assert isinstance(discover["signature"], str)
+    assert "bound method" not in discover["signature"]
+    assert discover["signature"].startswith("discover_module_paths(")
+    assert discover["docstring"] is not None