Keep the star visible at the distance that frames its system

Framing the whole system pushed the camera far enough back that the star
at the centre became a speck — about a pixel across for the Sun.

The cause is a constraint that cannot be tuned away. A star is sized
against its system's innermost orbit, because it must never swallow its
closest planet, while the camera is placed to frame the outermost ring.
In the solar system those differ by a factor of a hundred: at the distance
that fits Pluto in view, a disc that stays clear of Mercury is a pixel
across. No radius satisfies both, because the information genuinely does
not fit on one screen at that zoom.

So the disc stays honest to the orbits and the halo carries the
visibility. Light is not a surface: a glow that reaches past the innermost
orbit says the star is bright, not that it is large. Its extent is still a
multiple of the star — so a compact system keeps exactly the corona it had
— but floored against the framed radius, which is what the wide systems
needed.

The disc grows a little too: it may now reach 45% of the innermost orbit
rather than 35%, which still leaves clear space between the star's limb
and the closest orbit.

Also makes createGlowSprite take the extent it will draw rather than a
radius and a multiplier. The two were only ever multiplied together, and
how large a star's halo should be is not a property of the star — it
depends on how its system is framed, which is a decision that belongs with
the framing.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01WaySiNst4HhDXBHnMy8p5G

.junie/plans/nasa-star-map.md

@@ -311,3 +311,4 @@ Real photography where it exists, and a surface reasoned from measurements where
 - Replace the fixed distance-to-outermost-orbit multiple with a distance derived from the camera's vertical field of view and aspect, so what fits is a radius on screen rather than a guess.
 - Frame against the reference grid's outer ring, which is always wider than the outermost orbit, and leave an explicit margin around it.
 - Raise the framing ceiling far enough to hold the solar system out to Pluto in a portrait window; only companions hundreds of AU out reach it now.
+- Floor the star's halo against the framed radius, so a star sized against its innermost orbit still reads at the distance that frames its outermost one.