Link only the stars that are drawn

The jump-link graph linked the whole catalogue: 3.7 million links at 8 pc, 7.4-7.8 s in the
worker and a 443-515 ms frame on the main thread when they landed, and most of them between stars
that were neither drawn nor clickable. A graph request now carries the star field's drawn stars,
and the worker links only those, over an index of its own with cells as wide as the range. The
scene asks again once a new drawn set has held still for 250 ms.

The renderer is handed the graph's bounding sphere instead of computing it: three.js walked every
vertex on the main thread in the first frame that drew a new graph, 48-55 ms at 8 pc.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_016jxMkwA2rbicdGxHosecYi

src/app/shared/astro/jump-links.ts

@@ -214,12 +214,13 @@ export function minimumRangeBetween(index: StarNeighbourhood, fromId: number, to
 }
 
 /**
- * Every link within `rangePc` in the whole catalogue, each pair once, as vertex pairs ready to
- * draw: six floats a link, one end then the other.
+ * Every link within `rangePc` between two of the stars `index` holds, each pair once, as vertex
+ * pairs ready to draw: six floats a link, one end then the other.
  *
  * For drawing the graph, which is the only thing that wants all of it: routing asks for a star's
  * neighbours as it reaches that star and never builds this. Written straight into floats rather
- * than collected as link objects first, since at 8 pc there are 3.7 million links.
+ * than collected as link objects first, since at 8 pc the drawn stars alone have hundreds of
+ * thousands of links, and the whole catalogue 3.7 million.
  */
 export function jumpLinkSegments(index: StarNeighbourhood, rangePc: number): Float32Array {
   let vertices = new Float32Array(6 * 4096);