research integrating TM visualization directly in TOMs

[moira-andrews]

[sfoale]

I did a bit of research into how we can provide the functionality to embed the treasuremap visualisation into other applications. The standard way to do this kind of thing is to use a web component. Svelte has good support for compiling any component into a Web Component so this is the mechanism I suggest we use. Some initial reading: Svelte custom elements docs and the svelte:options reference.

Rough steps:

1. Explore the existing visualisation code: frontend/src/lib/components/visualization/AladinVisualization.svelte and the OverlayManager.svelte.
2. Create: something like frontend/src/viewer where the component will live separate from the main app. This will need a main svelte component, an API client and a utility to load Aladin Lite at runtime.
3. Write the Web Component: create something like GWTMSkymap.svelte using <svelte:options customElement>. This should accept graceid, alert-type, height etc. as HTML attributes and internally call the existing AladinVisualization and OverlayManager components once data has loaded.
4. Wire up the data: Fetch the required data from the exsiting API endpoints.
5. Set up a separate Vite build: we want a single self-contained .js file external sites can include, not the standard SvelteKit app build. Vite supports this via library mode.
6. Test in isolation: e.g. write a plain test-viewer.html file and embed the visualisation with something like