feat(cli,mkdocs): require site_name, fix nav paths, and echo serve URL

- Require `--site-name` when generating mkdocs.yml to ensure valid configs
- Inject site_name explicitly into generated mkdocs.yml
- Echo MkDocs serve URL (http://127.0.0.1:8000) before starting server
- Fix MkDocs nav emission to correctly resolve docs-relative paths
- Align MkDocs-related optional dependencies with a compatible, pinned set

These changes make MkDocs generation valid by default, improve UX when serving,
and prevent nav path and plugin compatibility issues.

pyproject.toml

@@ -42,8 +42,15 @@ doc-forge = "docforge.cli.main:main"
 
 [project.optional-dependencies]
 mkdocs = [
-    "mkdocs>=1.5.0",
-    "mkdocstrings[python]>=0.20.0",
+    "mkdocs==1.6.1",
+    "mkdocs-material==9.6.23",
+
+    "mkdocstrings==0.25.2",
+    "mkdocstrings-python==1.10.8",
+    "mkdocs-autorefs==0.5.0",
+
+    "pymdown-extensions==10.16.1",
+    "neoteroi-mkdocs==1.1.3",
 ]
 sphinx = [
     "sphinx>=5.0.0",