docs: clarify optional dependency in requirements

Co-authored-by: DeepSeek <service@deepseek.com>

Author: SilverRainZ

{{cookiecutter.name}}/docs/requirements.txt

@@ -1,7 +1,7 @@
 # {{ cookiecutter.generated_file_header }}
-
 # Documentation build dependencies.
 # Keep these out of pyproject optional-dependencies to avoid resolver issues.
+
 furo
 sphinx_copybutton
 sphinxcontrib-gtagjs
@@ -15,5 +15,9 @@ sphinxnotes-project
 sphinxnotes-comboroles
 {%- endif %}
 
+# NOTE: Not used by docs (docs import extension from ../src),
+# only to resolve its optional dependencies.
+{{ cookiecutter.full_name }}
+
 # CUSTOM DOCS DEPENDENCIES START
 # CUSTOM DOCS DEPENDENCIES END