Draw the system at true scale, drop the halo, and refuse to enter what is off screen

Three changes to what the system view claims, all of them the same claim: that
the sizes on screen mean something.

**The halo is gone.** It was a sprite sized against the arrival frame — 1.12 AU
for the Sun — so it stayed that wide as the camera closed in and ended up a flat
gradient filling the screen, over the photograph it was meant to dress. It
existed to keep the star visible at a framing that holds the whole system, which
is now handled in pixels instead.

**Bodies are drawn at their own radius.** The old marker size was exaggerated
and scaled to the system span, and clamped: Jupiter and Ganymede both ran past
the ceiling and were drawn at one radius, so every moon orbited inside its
planet, and Phobos and Triton sat entirely within Mars and Neptune. True scale
needs no rule against that — physics already puts a moon outside the planet it
orbits. What it costs is visibility at the arrival framing, where every body is
sub-pixel, so the scene floors each marker at 3 px on screen and holds a moon to
half its planet's drawn size. Measured in the Sun's system: at arrival, planets
3 px and moons 1.5 px, against 3 px for everything before; at Jupiter, the
planet 10.8 px at scale 1 with the Galilean moons on their orbits outside it.

The Sun is drawn at its own radius too. Every other star keeps a size derived
from its innermost orbit, because no stellar radius reaches the app — Gaia's
`radius_gspphot` is the obvious next fetch.

**A click cannot enter a system that is not on screen.** The picker tested depth
but not the frame, and a star's hit area is its drawn size plus a slop, so a
click in the last pixels of the view could fly into a system outside it, with
nothing on screen to explain where it had gone.

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

src/app/features/galaxy-system/star-field-renderer.ts

@@ -406,6 +406,11 @@ export class StarFieldRenderer {
    * needed: each star is tested against the size it is actually drawn at, so the hit area matches
    * what the user sees at every zoom level instead of being over-permissive up close and
    * sub-pixel at the far end of the camera's range.
+   *
+   * Only stars on screen can be picked. The hit area is the drawn size plus a slop of
+   * {@link PICK_NDC_SLOP}, and near an edge that slop reaches past the frame: a click in the
+   * last few pixels of the view used to be able to fly into a system whose star was outside it,
+   * with nothing on screen to explain where it had gone.
    */
   pickAt(pointerNdc: THREE.Vector2, camera: SceneCamera, aspect: number): number | undefined {
     // What a unit of angular size is worth on screen. Under perspective the field of view sets