Remove test from euclid and start a readme for plugins/ dir

Author: jaladh-singhal

plugins/README.md

@@ -0,0 +1,69 @@
+# IRSA MyST Plugins
+
+Custom [MyST](https://mystmd.org) plugins for the irsa-tutorials.
+
+## Building
+
+```bash
+cd plugins
+npm install
+npm run build
+```
+
+This bundles `src/notebook-gallery.mjs` into `dist/notebook-gallery.mjs`. Must *re-run* after any changes to `src/`.
+
+## Registering with MyST
+
+Add the built bundle to `myst.yml`:
+
+```yaml
+project:
+  plugins:
+    - plugins/dist/notebook-gallery.mjs
+```
+
+---
+
+## Plugin: `notebook-gallery` directive
+
+Renders a list of notebooks as a responsive grid of clickable cards. Each card shows a title and a one-sentence description pulled from a shared metadata file.
+
+### Metadata file
+
+The directive argument is a path to a YAML or JSON file (relative to the repo root) that lists notebook metadata. Each entry must have at least:
+
+| Field         | Type   | Description                                          |
+| ------------- | ------ | ---------------------------------------------------- |
+| `file`        | string | Path to the notebook relative to the repo root       |
+| `title`       | string | Display title shown in the card header               |
+| `description` | string | One-sentence summary shown in the card body          |
+
+Example `notebook_metadata.yml`:
+
+```yaml
+- file: tutorials/wise/wise_catalog_search.md
+  title: WISE Catalog Search
+  description: Search the AllWISE catalog using astroquery.
+- file: tutorials/euclid/1_Euclid_intro_MER_images.md
+  title: Euclid MER Images
+  description: Access and visualise Euclid Q1 MER mosaic images.
+```
+
+### Directive syntax
+
+````markdown
+```{notebook-gallery} notebook_metadata.yml
+tutorials/wise/wise_catalog_search.md
+tutorials/euclid/1_Euclid_intro_MER_images.md
+```
+````
+
+- The **argument** (on the opening fence line) is the path to the metadata file.
+- The **body** lists one notebook path per line (matching the `file` field in the metadata). Lines starting with `#` are treated as comments.
+
+### Error handling
+
+| Situation                           | Rendered output                                          |
+| ----------------------------------- | -------------------------------------------------------- |
+| Metadata file not found / unreadable | An `{error}` admonition with the bad path               |
+| Notebook path not in metadata        | A warning card: _⚠️ Unrecognised notebook_              |

tutorials/euclid/euclid.md

@@ -23,19 +23,4 @@ tutorials/euclid/merged-objects-hats-catalog/4-euclid-q1-hats-magnitudes.md
 tutorials/euclid/euclid-cloud-access.md
 tutorials/euclid/euclid_clusters_tutorial.md
 tutorials/euclid/Euclid_ERO.md
-```
-
-## notebook-gallery exception handling tests
-### Invalid notebook path
-```{notebook-gallery} notebook_metadata.yml
-tutorials/euclid/1_Euclid_intro_MER_images.md
-tutorials/euclid/does_not_exist.md
-tutorials/euclid/2_Euclid_intro_MER_catalog.md
-```
-
-### Invalid metadata path
-```{notebook-gallery} does_not_exist.yml
-tutorials/euclid/1_Euclid_intro_MER_images.md
-tutorials/euclid/2_Euclid_intro_MER_catalog.md
-tutorials/euclid/3_Euclid_intro_1D_spectra.md
 ```