Add card layout to tutorials/ and examples/ index pages

Mirrors the gallery landing page's tile pattern in the section index
pages, so each section reads the same whether you arrived via the
Gallery card or via the sidebar.

Thumbnails (getting_started.png, visium_mouse_brain.png) are
copied into the notebooks repo next to their respective notebooks.
Sphinx auto-copies them into _images/ at build time when referenced
from :img-top:. The lib's docs/_static/gallery/ thumbnails stay as
the source-of-truth for the landing page; consolidation can come
later if duplication becomes annoying.

Author: timtreis

examples/index.md

@@ -1,9 +1,23 @@
 # Examples
 
-Worked examples showing `spatialdata-plot` on real spatial-omics datasets.
-Use these to see how the API composes on data you'd actually analyse.
+Worked examples on real datasets you'd actually analyse.
+
+::::{grid} 1 2 2 2
+:gutter: 3
+
+:::{grid-item-card} Visium mouse brain
+:link: visium_mouse_brain
+:link-type: doc
+:img-top: visium_mouse_brain.png
+
+Render H&E tissue, overlay spots, color by gene expression and by cluster,
+and finish with a publication-style figure.
+:::
+
+::::
 
 ```{toctree}
+:hidden:
 :maxdepth: 1
 
 visium_mouse_brain

examples/visium_mouse_brain.png

@@ -1,10 +1,23 @@
 # Tutorials
 
-End-to-end workflows demonstrating `spatialdata-plot` on real spatial-omics
-datasets. Each tutorial walks through loading a published dataset, layering
-spatial elements, and styling a publication-ready figure.
+Entry-point material for learning the API on synthetic data.
+
+::::{grid} 1 2 2 2
+:gutter: 3
+
+:::{grid-item-card} Getting started
+:link: getting_started
+:link-type: doc
+:img-top: getting_started.png
+
+The fluent `.pl` API, layering, and styling on the in-memory `blobs`
+dataset. Ideal first read.
+:::
+
+::::
 
 ```{toctree}
+:hidden:
 :maxdepth: 1
 
 getting_started