py(deps[docs]): add sphinx-design, annotate doc dependencies with site URLs

why: sphinx-design is needed for grid cards in the documentation
landing pages and section indexes. Doc-site URLs added as inline
comments for quick reference when managing dependencies.
what:
- Add sphinx-design to docs and dev dependency groups
- Annotate all doc dependencies with their documentation URLs

Author: tony

pyproject.toml

@@ -79,6 +79,7 @@ dev = [
   "sphinxext-opengraph",
   "sphinx-copybutton",
   "sphinxext-rediraffe",
+  "sphinx-design",
   "myst-parser",
   "linkify-it-py",
   # Testing
@@ -114,6 +115,7 @@ docs = [
   "sphinxext-opengraph",
   "sphinx-copybutton",
   "sphinxext-rediraffe",
+  "sphinx-design",
   "myst-parser",
   "linkify-it-py",
 ]