feat(mcp): add MCP JSON renderer and CLI support, update tests accordingly

- Add MCPRenderer to generate MCP-native JSON bundles (index.json, nav.json, modules/*.json)
- Expose MCPRenderer via public API and CLI (`generate-mcp` command)
- Replace Markdown-based MCP output with structured JSON resources
- Update MCP renderer type stubs to match new JSON-based implementation
- Refactor MCP tests to validate JSON content, bundle structure, and navigation
- Fix MCP module coverage test to use explicit project_root for reliable discovery

docforge/renderers/mcp_renderer.pyi

@@ -1,31 +1,26 @@
 from pathlib import Path
-from typing import Iterable
+from typing import Dict, List
 
 from docforge.models import Project, Module, DocObject
 
 
 class MCPRenderer:
-    """
-    Renderer that emits MCP-compatible documentation resources.
-    """
+    """Renderer that emits MCP-native JSON resources from docforge models."""
 
     name: str
 
     def generate_sources(self, project: Project, out_dir: Path) -> None:
-        """Generate MCP resources for the given project."""
+        """Generate MCP-compatible JSON resources and navigation for the project."""
 
-    def _write_module(self, module: Module, out_dir: Path) -> None:
-        """Write a single module as an MCP resource."""
+    def _write_module(self, module: Module, modules_dir: Path) -> None:
+        """Serialize a module into an MCP JSON resource."""
 
-    def _render_module(self, module: Module) -> str:
-        """Render a module and its contents into a text document."""
+    def _render_module(self, module: Module) -> Dict:
+        """Render a Module into MCP-friendly structured data."""
 
-    def _render_object(
-        self,
-        obj: DocObject,
-        level: int,
-    ) -> Iterable[str]:
-        """Recursively render a documented object and its members."""
+    def _render_object(self, obj: DocObject) -> Dict:
+        """Recursively render a DocObject into structured MCP data."""
 
-    def _module_resource_path(self, module: Module) -> Path:
-        """Compute the MCP resource path for a module."""
+    @staticmethod
+    def _json(data: Dict) -> str:
+        """Serialize structured data to formatted JSON."""