docs: add shape and label styling tutorial (#16)

* Add shape and label styling tutorial

New tutorials/styling_shapes_and_labels.ipynb covering the fill/outline
styling surface of render_shapes and render_labels on the blobs dataset:

- fill_alpha for both shapes and labels
- the outline bool toggle (restored for shapes and labels in #750) with
  outline_width / outline_color / outline_alpha
- hollow shapes (transparent fill + outline)
- scale for resizing shape geometries about their centroids
- segmentation boundaries on labels via outline + contour_px, and the
  translucent-fill-plus-outline overlay over an image

Executed against spatialdata-plot v0.4.1; committed with outputs. Adds the
gallery card + toctree entry and a thumbnail. Deliberately leaves color=/
palette/groups to the colour tutorial and points styling to as_points.

* docs(styling): fix labels default (fill_alpha=0.4 not solid), make overlay demo go below default, drop internal jargon

* docs(styling): add double-outline section, document column outlines

Add a 'Two outlines — outer and inner' section demonstrating the
(outer, inner) two-tuple form of outline_width/color/alpha, which the
tutorial previously never showed. Note column-based outline colouring
in the summary (points to the Colouring tutorial; needs a table-annotated
element, so no blobs demo). Renumber sections and refresh objectives.

Claude-Session: https://claude.ai/code/session_01U9J5GSXR4XGjPMaQQR5iSj

* docs(styling): new thumbnail capturing the full styling story

Replace the dark single-facet label overlay with one coherent scene:
crimson/gold double-outlined translucent polygons (fill opacity + the
new double outline) over white segmentation contours on the blobs image
— shapes styling and label boundaries in one frame.

Claude-Session: https://claude.ai/code/session_01U9J5GSXR4XGjPMaQQR5iSj

Author: timtreis

_static/img/styling_shapes_and_labels.png

@@ -93,6 +93,16 @@ time, images rasterized for the window only, and how it differs from
 `bounding_box_query`.
 :::
 
+:::{grid-item-card} Styling shapes and labels
+:link: /notebooks/tutorials/styling_shapes_and_labels
+:link-type: doc
+:img-top: /notebooks/_static/img/styling_shapes_and_labels.png
+
+Control how shapes and labels are drawn: `fill_alpha`, the `outline`
+toggle with `outline_width`/`outline_color`/`outline_alpha`, hollow
+shapes, `scale`, and segmentation boundaries via `contour_px`.
+:::
+
 ::::
 <!-- gallery-cards-end -->
 
@@ -109,4 +119,5 @@ scalebars
 marker_shapes
 multichannel_images
 cropping
+styling_shapes_and_labels
 ```