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

@@ -70,6 +70,7 @@ dev = [
   "sphinxext-rediraffe",
   "sphinx-argparse",
   "myst-parser",
+  "sphinx-design",  # https://sphinx-design.readthedocs.io/
   "linkify-it-py",
   # Testing
   "gp-libs",
@@ -103,6 +104,7 @@ docs = [
   "sphinxext-rediraffe",
   "myst-parser",
   "linkify-it-py",
+  "sphinx-design",  # https://sphinx-design.readthedocs.io/
 ]
 testing = [
   "gp-libs",